LIBRARY
OF THE
UNIVERSITY OF CALIFORNIA.
Class
Wireless Telegraphy
Its History, Theory and Practice
BY
A. FREDERICK COLLINS
Published by the
McGraw-Hill Book. Company
Ne
to the Book Department* of tKe
McGraw Publishing Company Hill Publishing Company
Bobliahers of Books for
Electrical World The Engineering" and Mining Journal
TKe Engineering Record Power and The Engineer
Electric Railway Journal American Machinist
miiHi
NEW YORK
McGRAW PUBLISHING COMPANY
1905
Wireless Telegraphy
Its History, Theory and Practice
BY
A. FREDERICK COLLINS
Of THE
UNIVERSITY
OF
NEW YORK
McGRAW PUBLISHING COMPANY
1905
cl
Copyrighted, 1905
by the
McGRAw PUBLISHING COMPANY
NEW YORK
PREFACE.
Nearly a decade has now elapsed since the wireless telegraph
made its spectacular appearance on the horizon of progressive
achievement, and in these passing years it has come to be a factor
of the first magnitude in the scheme of social and commercial
economics which forms the foundation of our complex mode of
living.
As an example of occult manifestations by the most subtle of
nature's forces it stands vividly at the head of this class of
phenomena, and the skilled labor it has called forth, that longer
distances might be bridged, greater accuracy assured, swifter work-
ing effected, and, above all, the correlation of the invisible and
elusive waves which would render selectivity a concrete fact, may in
a small measure be determined by a perusal of these pages.
Since it frequently happens that didactic treatises fall into the
hands of the untaught and the simplest of texts are sometimes
found useful by the most highly trained specialist, it was pro-
posed that all the various phases of the subject under consideration
should receive due attention and, by connecting them in series,
a complete and logical account would necessarily follow and one
that would bring the state of the art down to the present time.
For- this reascm a brief historical retrospect takes precedence
at the beginning of nearly every chapter, and then, in order to
fulfil in sequence the conditions cited above, the theoretical deduc-
tions, experimental physics and finally the practical workings are
given, and it is believed that by pursuing this course of treatment
the book will find a hitherto unoccupied niche in the bibliography
relating to wireless telegraphy.
In conclusion I wish to acknowledge my indebtedness to my
friend, Dr. James E. Ives, for many consequential details herein
enumerated, and which should, in virtue of his wide experience in
the analysis and synthesis of electric wave action, make these por-
tions invaluable to the student as well as to the advanced worker;
and my thanks are also clue to my brother, Dr. T. Byard Collins
and to my wife, both of whom have greatly assisted in its
preparation by reading the proofs and checking up the data.
A. FREDERICK COLLINS.
New York City, April, 1905.
CONTENTS.
CHAPTER I.
ETHER
PAGE.
HISTORICAL 1
THEORETICAL 5
Function of the Ether 5
Constants of the Ether 10
CHAPTER II.
WAVE MOTION
THEORETICAL 11
Molecular Undulations 11
Transverse Vibration 13
Light Wave Length 14
Reflection 16
Refraction 16
Polarization 17
CHAPTER III.
ELECTRIC WAVES
HISTORICAL 20
EXPERIMENTAL 21
Hertz's Apparatus 28
Reflection 29
Rectilinear Propagation 30
Refraction 30
Polarization 32
Free Electric and Sliding Half -Waves 33
CHAPTER IV.
DISRUPTIVE DISCHARGE
HISTORICAL 36
PHYSICAL 38
Forms of Discharges 38
Discharge Through Dielectrics 39
Color, Size and Shape of Discharges 40
Striking Distance 42
Action of Ultra Violet Light 44
Direct and Alternating Current Effects 45
vi CONTENTS.
CHAPTER V.
ELECTRIC OSCILLATIONS
PAGE.
HISTORICAL 47
THEORETICAL 48
Low Frequency Currents 48
High Frequency Currents 49
Analogue of Electric Oscillations 49
Properties of Electric Oscillations 50
Transformation 52
Rate of Radiation of Energy 53
Decrement of Oscillations 54
Skin Effect in Oscillators 55
CHAPTER VI.
OSCILLATORS
PHYSICAL 56
Oscillators 56
Oscillator Systems 56
Hertz's Oscillator 57
Righi's Oscillator 58
Lodge's Oscillator 58
Multiplex Oscillator 59
Dumbbell Oscillator 59
Bose's Oscillator 60
Experimental Oscillator 60
Marconi's Oscillator 61
Open and Closed Systems 61
Symmetrical and Dissymmetrical Systems 63
CHAPTER VII.
CAPACITY, INDUCTANCE, AND RESISTANCE
HISTORICAL 64
Capacity 64
Inductance 65
Resistance 66
THEORETICAL 66
Capacity Defined 66
Inductance Defined 67
Resistance Defined 68
Effect of Constants on Oscillations 69
Formulae for Calculating Constants 70
Calculation of Oscillator Dimensions 71
Measurements 71
Capacity 72
Capacity of an Aerial 74
Inductance 75
Inductance of an Aerial 76
Resistance 77
CHAPTER VIII.
MUTUAL INDUCTION
HISTORICAL , 78
THEORETICAL 80
Induced Currents 80
CONTENTS. vii
PAGE.
Primary and Secondary Currents 82
Theory of the Induction Coil 83
Permeability 83
Hysterisis 84
Mutual Induction 84
Function of the Condenser 85
Optimum Capacity 87
Calculating the Potential of a Coil 88
Forms of Coils " 89
CHAPTER IX.
INDUCTION COILS
HISTORICAL 92
PRACTICAL 95
Primary Coils 96
Secondary Coils 97
Insulation 99
Assembly of Parts 100
Sources of E. M. F 100
Selection and Care of a Coil 100
Types of Coils 102
Ordinary Coil 102
Modern Coil 102
Foote Pierson Pelta Coil 103
Lodge Muirhead Coil 103
Kinraide Coil 103
Braun-Siemens and Halske Coil 103
Slaby-Arco Coil 103
Fessenden Coil 104
Queen & Co. Meter Spark Coil 105
CHAPTER X.
INTERRUPTORS
PRACTICAL : 107
Single Vibrating Interruptor 108
Double-Contact Interruptor 109
Double Spring Interruptor 110
Independent Interruptor Ill
Mechanical Reciprocating Interruptor 112
Mechanical Rotating Interruptor 113
Mercury Turbine Interruptor 114
Electrolytic Interruptor 116
Liquid Interruptor 119
Rotary Interruptor 120
Disruptive Discharge Interruptor 121
. Rotary Converter Interruptor 122
Mercury Vapor Interruptor 125
CHAPTER XL
OSCILLATING CURRENT GENERATORS
PRACTICAL 127
Holtz-Toepler Machines 128
Fleming Transformer 130
Tesla Oscillator 130
Elihu Thomson Apparatus 134
viii CONTENTS.
CHAPTER XII.
ELECTRIC WAVE ACTION
PAGE*
HISTORICAL , 136
THEORETICAL 136
EXPERIMENTAL 140
Branly's Experiments 140
Koepsel's, Guthe's and Tommasina's Researches 142
De Forest and Smyth's Investigations 143
Testing the Coherer 143
CHAPTER XIII.
ELECTRIC WAVE DETECTORS
PRACTICAL 14$
Calzecchi Tube 145
Hertz Resonator 145
Branly Radio-Conductor 145
Lodge Coherer 147
Other Detectors 147
Marconi Coherer 149
Experimental Coherer 150
Slaby-Arco Coherer 150
Braun 151
Blondel Regenerable Coherer 153
Schaffer Anti-Coherer 153
Branly Tripod Coherer 154
Castelli Coherer 154
Fessenden Magnetic Detector 154
Marconi Magnetic Detector : 155
DeForest Electrolytic Responder 157
Lodge Mercurial Coherer 158
Marconi Magnetic Detector (Second Form) 159
Fessenden Hot-Wire Barretter 160
Fessenden Liquid Barretter 161
Testing Boxes or Buzzers 162
CHAPTER XIV.
TRANSMITTERS
HISTORICAL 163
PRACTICAL 164
Classification of Transmitters 165
Marconi Transmitter (First Form) .' 166
Marconi Transmitter (Second Form) 166
Lodge Transmitter 167
Slaby-Arco Transmitter (First Form) 168
Slaby-Arco Transmitter (Second Form) 169
Guarini Transmitter (First Form) 171
Guarini Transmitter (Second Form) 173
Marconi Transmitter (Third Form) 174
Braun Transmitter 175
Marconi Transmitter ( Fourth Form ) 176
CONTENTS. ix
PAGE.
Popoff-Ducretet Transmitter 178
DeForest Transmitter 178
Fessendeii Transmitter 179
Branly-Popp Transmitter 180
Cervera Transmitter 182
Lodge-Muirhead Transmitter 182
Bull Transmitter 183
Marconi Cableless Transmitter 184
CHAPTER XV.
RECEPTORS
HISTORICAL 185
PRACTICAL 186
Classification of Receptors 186
Popoff Receptor 187
Marconi Receptor ( First Form ) 188
Marconi Receptor ( Second Form ) 190
Lodge Receptor 191
Slaby-Arco Receptor 191
Braun Receptor 192
Marconi Receptor ( Third Form ) 194
Guarini Automatic Repeater 195
Marconi Receptor ( Fourth Form ) : 197
Fessenden Receptor 198
Popoff-Ducretet Receptor 200
DeForest-Smythe Receptor 201
Cervera Receptor 202
' Branly-Popp Receptor 203
Lodge-Muirhead Receptor 204
Bull Receptor 207
Marconi Cableless Receptor 207
CHAPTER XVI.
SUBSIDIARY APPARATUS
PRACTICAL 210
KEYS 210
Marconi Key - 210
( a ) Braun Key 211
(b) Braun Key 211
Ducretet Key 212
Fessenden Key 213
DeForest Key 213
Lodge-Muirhead Key 214
Lodge-Muirhead Buzzer 215
CONDENSERS 216
Tesla Oil Condenser 216
Braun Cylindrical Condenser 216
Adjustable Mica Condenser 217
TRANSFORMERS 218
Braun High-Frequency Transformer 218
Marconi Low Potential Transformer . . 219
CONTENTS.
PAGE.
DE-COHEKEBS 220
Marconi Tapper 221
Braun Tapper 222
Guarini Tapper 223
Collins Magnetic De-Coherer 223
RELAYS 223
Ordinary Relays 223
Polarized. Relays 224
INDICATORS 226
Morse Register 227
Telephone Receivers 228
Siphon Recorders 229
TUNING COILS 230
CHOKING COILS 231
POLARIZED CELLS 231
SCREENING CASES 232
ALPHABETIC CODES . , . 232
CHAPTER XVIT.
AERIAL WIRES AND EARTHS
HISTORICAL 234
THEORETICAL ' 234
PRACTICAL 238
Methods of Suspension : 239
Forms of Aerials 240
Lodge Capacity Aerial 241
Guarini Sheathed Aerial 241
Jegou Differential Aerial 241
Marconi Aerial (Second Form) . . 242
Slaby-Arco Direct Earthed Aerial 243
Braun Artificial Earth 244
DeForest Mast and Aerial 244
Fessenden Wave Chute 245
Kite-Sustained Aerials 247
Marconi Cableless Station Aerial . 252
CHAPTER XVII I.
RESONANCE
HISTORICAL 258
THEORETICAL , 259'
EXPERIMENTAL 261
Simple Resonance 261
Sympathetic Resonance 262
Determination of Periodicity 264
Apparatus for Plotting Resonance Curves 265
Relation of Co-efficients to Resonance ... v 265
Tuning Closed to Open-Oscillator Circuits 267
Tuning Resonator Circuits . 267
Resonance in Wireless Telegraphy 268
CONTENTS. xi
CHAPTER XIX.
SYNTONIZATION
PAGE.
HISTORICAL 26!)
PRACTICAL 270
Lodge Tuned System 270
Slaby-Arco Multiple System 272
Marconi Syntonic System (First Form) 273
Marconi Syntonic System ( Second Form ) 274
Braun Resonance System 274
Fessenden Selective System 275
Tesla Duplex System 276
Stone Multiplex System 277
Bull Synchronized System 280
CHAPTER XX.
WIRELESS TELEPHONY
Conductivity Method 286
Inductivity Method 286
Electric Wave Method 287
Bell Radiophone 287
Ruhmer Photo-Electric Telephone 288
Collins Wireless Telephone 292
CHAPTER I.
ETHER.
To understand the fundamental principles involved in trans-
mitting electric waves without connecting wires we are confronted
at the very outset with the postulates of that branch of physics deal-
ing with transcendental matter.
By transcendental matter we mean the substance of which the
ether is composed and we cannot, by any known physical method,
determine its constituency, although this has been attempted. By
the term electric waves we differentiate waves emitted by electricity
and electricity itself.
HISTORICAL.
For at least a thousand years B.C. philosophers advanced the
hypothesis of a medium in the form of a substance or attenuated
fluid filling interstellar space and all space in masses and between
molecules and atoms not otherwise occupied by gross matter.
These speculations, though not verified by experiment, were ad-
vanced for the purpose of satisfying the demand occasioned by a
particular phenomenon, for it frequently occurred that an ex-
planation or a theory would be found wanting, if not, indeed,
utterly untenable, without assuming the existence of a connecting
medium ; other thinkers advocated a universal ether in virtue of
the requirements of their metaphysics, as, for instance, where its
presence was deemed a necessary factor in the extension of matter,
or the postulate that all space must be filled with something, since
nature and a vacuum are incompatible.
Oppositely arrayed were those who proclaimed that matter
could act on other matter through space without intervening mat-
ter to transmit the energy, i.e., action without physical contact ; and
by them this was considered a rational philosophy. Without the
evidence of an experimental nature to justify the claims of either
2 WIRELESS TELEGRAPHY.
faction, the problem remained practically unsolved throughout all
the succeeding centuries until the dawn of the nineteenth, when
the cloud of obscurity overhanging it began to rise.
The question was, from its incipiency, a constant theme for dis-
cussion and bitter debate, and even in 1(550, when Sir Isaac Newton
evolved his theory of universal gravitation, there were still the
opposition parties, who were now resolved into the Cartesians, or
followers of Descartes, who resisted the onward wave of
"action at a distance," and the Newtonians, who believed that
intervening matter was not essential to the transmission of energy
from one body to another removed by distance. This was a rather
curious phase of the discussion, for it would seem from Newton's
own letters that he was quite firm in his belief of the actual
existence of this attenuated, subtle substance, notwithstanding his
followers were opposed to it.
Nearly one hundred years after, or in the middle of the eigh-
teenth century, Father Boscovitch promulgated his doctrinal theory
that the laws governing all matter, including their inherent char-
acteristics of physics, chemical affinity, electricity, and magnetism,
could be explained by mutual attractions and repulsions, but to fire
he gave a special attribute — that of an essence — to account for un-
familiar phenomena. During the next fifty years the erratic phi-
losophy of the priest had become almost universally accepted as the
final solution of action at a distance through absolute vacuum, or, as
Sir William Thompson, now Lord Kelvin, tersely puts it, "matter
acting where it is not," so that the dissolution of the ether was
thought by scientists to be complete and the question forever settled,
and this in the face of the fact that Christian Huygens, a Dutch
mathematician and physicist, had in 1678 worked out his undulatory
theory of light and an ether by which he was enabled to account for
all its various phenomena. Huygens's is the only tenable theory
in the revelations of modern science, but it was shelved for that of
Boscovitch and was doomed to obscurity until the wheel revolved
and it again came uppermost when that eminent experimentalist,
Michael Faraday, in 1845, made a series of tests in an effort to
prove that the laws which govern light as elucidated by Huygens—
in whose undulatory theory he had the utmost confidence^ — were
the same as those of magnetism. This he successfully accomplished
by the rotation of the plane of polarized light under the action of
ETHER. 3
magnetism, the transparent glass employed for the purpose being
quite heavy and of his own manufacture.
This discovery did not lead to such important practical results in
applied science as some of Faraday's earlier discoveries, but it has
been of infinitely greater scientific value in establishing the unity of
an all-pervading medium, ether, upon which is based the complete
evidence that electricity and magnetism are propagated by, in, and
through the same substance which transmits the undulatory waves
of light as Huygens had proposed nearly two hundred years before.
It is true that earlier in the nineteenth century, before Faraday's
experimental researches, a reaction had partially set in regarding
the merits of Boscovitch's action at a distance and Huvgens's lumi-
niferous ether ; and the latter, which had been so utterly rejected the
preceding century, was now to have an inning and the former's
pseudo-tenets relegated to the dead past. But it was Faraday's
results that encouraged belief in the existence of an ether, and it
has grown stronger through the deductions based upon his experi-
ments by others who have repeated or enlarged upon them, and the
impetus Faraday gave to the Huygens theory has changed in the
last fifty years the trend of scientific opinion completely from
action at a distance to that of matter acting only where matter is.
Now also was Descartes and his law of vortices in the ascendency
after having lain dormant for many years.
The empirical evidence Faraday accumulated was entirely
sufficient for the complete acknowledgment of the existence
of an ether, and that electricity, magnetism, and light were
propagated by and through the same medium, but by many of his
contemporaries his classical experiments were not accepted without
the proverbial grain of salt. A few years later Faraday had a
champion who developed his electro-magnetic theory of light mathe-
matically and with such consummate skill and precision that they
have not only withstood the test of time, but every crucial test which
has been applied to them, and every discovery bearing on the sub-
ject has proven the correctness of their views.
In 1861 James Clerk-Maxwell systematized Faraday's concep-
tion, which is now known as the Faraday-Maxwell electro-magnetic
theory of light, which means, in its simplest form, that light, elec-
tricity, and magnetism are transmitted by the same ether through
which they travel with an identical rate of speed. Maxwell, by a
4 WIRELESS TELEGRAPHY.
system of Le Grange's co-ordinates, determined accurately the rela-
tions between the various phenomena it included. The number of
converts to the doctrine of transcendental matter were now greater
than had been made in all the preceding centuries, for Maxwell's
equations gave a tangibility to the subtle substance such as it had
never known before. There were those of course who still re-
fused to be convinced and who still clamored for such proof as could
only be obtained by decisive experiment.
The deductions of Maxwell were now taken up eagerly and
analyzed by such eminent scientists as von Helmholtz, Kelvin,
and many others, all of whom, starting with the well-knowr
laws of light, electricity, and magnetism, were led to conclude from
their own results the correctness of the Faraday-Maxwell theory,
and the final analysis of all tended to prove the actuality of one
ether. This was sufficient to account for all the varied phenomena
such as the rectilinear propagation of light, radiant heat, electro-
kinetics, and the curved lines of magnetic force.
The name of the lamented Heinrich Hertz should have been
added to those above written, for it remained for him alone to
establish experimentally" the proof of Maxwell's deductions. His
methods, like Faraday's, were physical rather than theoretical. The
tremendous amount of labor involved in probing for the truth
about ether, and the infinite pains required to obtain absolute, un-
deniable proof of it, may be understood by looking backward again
to the laborious task Faraday performed in showing experimentally
that the undulatory theory of light and his own curved lines of force
were related, and that, therefore, the ether transmitting them
must be the same. Maxwell then assumed the arduous duties entail-
ing the verification of Faraday's researches mathematically, and
finally Hertz utilized the equations of Maxwell and reversed the
order of Faraday's experiment demonstrating the existence of
stationary electric waves and that the time constant of their propa-
gation in ether was identical with that of light. This he did in
1888 at Karlsruhe, Germany, and his experiments, simple as the
laws governing the action of the electric waves they represent, and
as grand in their sublimity as the scientific world has ever known,
settled conclusively and finally the existence of an ether and laid
the foundation for a commercial enterprise that has so recently
startled the world in wireless telegraphy.
ETHER.
FIG. 1. — POLARIZATION OF ETHER.
(According to Helmholtz.)
THEORETICAL.
Hertz, in his great work, "Electric Waves/' has thoroughly
sifted the various viewpoints assumed by recent scientists for an
ether fulfilling all the functions required of it, and concludes with a
concise statement showing the difference in the views held by
Maxwell and those of Helmholtz. According to Helmholtz the
attractions between two separate bodies A and B, Fig. 1, is based
upon two factors, the first by direct action between A and B, repre-
sented by the arrows, and second by
the changes in the ether represented
by the intervening rectangles. Sup-
posing that the black portion of A
is positively charged, the force ex-
erted directly on B will be negative,
as indicated by the ruled portion;
the intervening matter, be it the
ether or other substance shown by
the rectangles, will be polarized,
that is, the portions nearest A will be negative and the opposite
sides will be positive, and these forces acting and reacting on the
subsequent matter on reaching B charge it negatively. According
to Poisson this polarization of the ether is of a magnetic nature, and
upon this deduction he developed his theory of statical magnetism ;
Mosotti assumed them to be electrical, and Helmholtz, combining
these two hypotheses, formulated a theory embracing all the phe-
nomena of electro-magnetism. This theory postulates that if from
the space C the ether be removed, forming an absolute vacuum, the
positive and negative forces will continue to exist as shown by the
arrows, but, since there is no matter, polarization cannot take place.
Maxwell, according to Hertz, agrees with Helmholtz in that
the polarizations of the ether are actually present, but not that
these polarizations are due to the force of A acting on B, and
Maxwell does not assume that the distant forces exist, hence A and
B represent nothing, and that the polarization is the only factor
present, as shown in Fig. 2, and it is this cause to which we may
trace all the effects of molecular and transcendental matter we are
acquainted with. It will be seen that if all the ether is removed
from the space C, Fig. 2, according to Maxwell, not only would the
polarizations not be manifested, but the electro-magnetic forces
6
WIRELESS TELEGRAPHY.
Fio. 2. — POLARIZATION OP ETHER.
(According to Maxwell.)
producing them would also not be present. This is Maxwell's
theory upon which he based his system of equations, and this is the
theory Hertz employed, with some few practical modifications,
in his experiments. Faraday laid
the corner-stone for this evolution
of etheric polarizations. Maxwell
was the architect who drafted the
plans for its consummation, but
Hertz was the builder, and when
he had finished his grand work
the first absolute proof of a ma-
terial ether rose before men, a
mighty masterpiece; so complete
were his classical investigations that Ernest Haeckel, the great evo-
lutionist, proclaimed that there would now be just as much reason
to deny the existence of molecular matter as to deny the existence
of the more subtle transcendental ether, and he lamented the fact
that, as there were metaphysicians who denied the molecular theory
of matter, as Berkeley and Hume, there were still a few philosophers
of the abstract who denied the existence of ether.
Hertz commenced his researches in 1879, when the Berlin Acad-
emy of Science offered a prize for the solution of a problem show-
ing polarizations in a non-conductor or dielectric to be the result
of electro-magnetic induction, but it was not until 1886 that
he was able to see his way clear to solving it. These remarkable
achievements will be fully treated in the succeeding chapters, for
Hertz's work embraces a whole series of exceedingly vital proposi-
tions, among them being the proof of the electro-magnetic theory
of light, the proof of the existence of an ether, the discovery of
stationary electric waves, the mode of producing electric waves by
means of a spark-gap, and the manifestation of electric waves by
means of a detector, all of those enumerated, but especially the
two latter discoveries, forming the basis of the subject herein
treated, wireless telegraphy. The sum of the knowledge advanced
by all the workers has given us the following conception of what
ether is, its functions, and we already know some of its uses.
But, after all is said, it must not be supposed that the nature
of ether is really known ; for that matter, we do not know positively
the real nature of molecular matter, but we do know many of the
laws governing the latter and some of the laws of the fornler, and
ETHER. 7
with these for the present we must be content. Slowly but surely
our knowledge of the laws of both are being enlarged and new laws
are occasionally discovered or more accurately determined, and all
this is of the greatest importance. As we have seen, the views of
those thinkers who have bended their energies toward a possible
solution of the ether mystery do not always coincide; more fre-
quently they appear to contradict each other, so that one is at a loss
to choose between them, but the following points will serve to show
the trend of scientific opinion.
Starting out with the now universally accepted idea that a
cosmic ether pervades all space not otherwise taken up by molecular
matter, and accepting Maxwell's postulates as gospel truths, we
are next confronted with the question of its structure. By some it
is believed to be a homogeneous corpuscular body, while others
conceive it to be a continuous substance. By those who hold to
the continuous theory, it is pointed out that the opposite theory of
etheric corpuscles is defective, for it must then be supposed that
there is another ultra-etheric medium between the corpuscles and
so on to infinity.
In behalf of the corpuscular theory, it has been advanced that
the corpuscles of ether, though of a uniform size, need not neces-
sarily be spherical, but of any shape permitting them to conform
to each other without leaving any intermediate space. The net
product would be then, to all intents and purposes, a continuous
substance. The consistency of ether calls for another subdivision
of opinion, for by some it is considered gaseous, by others a liquid,
and again by some others a solid. Again, probably it is none of
these, though each in turn serves as an analogue for its actions. In
popular lectures it is often likened to a jelly, and, though crude,
this offers a very good illustration of the elasticity and incom-
pressibility of the ether.
As a substance it is so high in the scale of matter that we cannot
sense it, nor have we any instruments sensitive enough to recognize
it. A conception may be obtained from Faraday's1 statement rela-
tive to the fourth state of matter. In 1816 he was conducting his
researches along these lines, and the expression he employed may
assist in elucidating the vast difference between gross matter and
ethereal matter ; he said, speaking of radiant matter : "If we conceive
a change as far beyond vaporization as that is above fluidity, and
'Dr. Bence Jones's Life and Letters of Faradav.
8 WIRELESS TELEGRAPHY.
then take into consideration also the proportional increased ex-
tent of alterations as the changes rise, we shall, perhaps, if we
can form any conception at all, not fall short of radiant matter;
and as in the last conversion many qualities were lost, so here
many more would disappear. As we ascend from the solid to the
fluid and gaseous states physical properties diminish in number
and variety, each state losing some of those which belong to the
preceding state; when solids are converted into fluids all varieties
of hardness and softness are necessarily lost. Crystalline and other
shapes are destroyed. Opacity and color frequently give way to a
colorless transparency and a general mobility of particles is con-
ferred. Passing onward to the gaseous state, still more are the
evident character of bodies annihilated. The immense differences
in their weight almost disappear, the remains in the difference in
color that were left are lost. Transparency becomes universal.
They now form but one set of substances and the varieties of den-
sity, hardness, opacity, color, elasticity, and form which render the
number of solids and fluids almost infinite are now supplied by a
few slight variations in weight and color."
How true is this of molecular and transcendental matter! It
is evident if we could conceive a matter as many times removed
from radiant matter as the latter is from solids we would have a
substance almost as far beyond our analytical powers as ether itself.
The distinction that some physicists have made between ether and
molecular matter is to class the former as imponderable and the
latter as ponderable; this is evidently erroneous, for, though the
specific gravity of ether is so slight as to be beyond the sensibility
of the most delicate testing instrument, yet as a substance it must
have weight, and this has been computed — from the energy of the
light waves through it1 — to be approximately over fifteen trillion
times lighter than the air, or, in popular language, a sphere of ether
the size of our earth would weigh only 250 pounds.
Maxwell has estimated its density to be Looo.ooo.oooS.ooo.ooo.ooo that
of water, and its rigidity to be rooo.oo^.ooo.ooo that of steel- Having
density and weight, ether and matter have, essentially, properties
in common with each other, and this is the more easily understood
if we consider Lord Kelvin's hypothesis of matter.
An atom of gross matter, according to this beautiful deduction,
^ebedew, Experiments on Radiation Pressure.
ETHER. 9
had not always a distinct entity, but originated in a minute
portion of the ether attaining a whirling motion, and in virtue of
the vortex so formed it became a particle of rigid matter — an
entity in itself. Although the ether is extremely tenuous, the vortex
motion will give it all the physical properties of matter such as
rigidity, stability, density, and weight.
As an analogue of the ether metamorphosed by vortex motion
into an atom of matter, vortex rings formed of smoke in the air
may be given, as they are familiar objects and may be easily pro-
duced. It must be remembered, however, that smoky air rings are
excessively crude when compared with ether vortex rings or atoms,
for the air is a very imperfect medium, whereas ether is absolutely
perfect ; for this reason air-vortex rings increase in size and decrease
in energy and ether- vortex rings remain absolute and constant, and
so, when once set in motion become atomic matter, and, when thus
transformed, cannot, by any method known to man, be destroyed.
As Oliver J. Lodge says, this ether offers practically one con-
tinuous substance which can vibrate as light, which may be sheared
into positive and negative electricity, which in whirls constitutes
atomic matter, which transmits energy by polarization instead of
impact and is the primary cause of every action and reaction of
which matter is capable.
In however many respects physicists may disagree as to the
nature of ether, they stand a unit in agreeing that it is in a
state of continual unrest. According to Plato ether derives its name
from the Greek term, signifying perpetual motion. Likewise are
these thinkers agreed as to the ether's incompressibility, which may
be regarded as infinite, although, according to Fresnel, in the pres-
ence of gross matter there is an attraction between the ether and
the atoms of matter, readily accounted for in the light of Kelvin's
hypothesis, which results in some of the ether forming a closer
affinity for, or clinging to and surrounding each individual atom like
the sugar coating of a pill. This is what Nikola Tesla terms bound
ether, and is a part of the atom to which it adheres and travels about
with it.
The relation of bound ether to electricity does not particularly
concern wireless telegraphy — that is another question — but it is
the radiation of waves emitted by electricity through and by free
ether that here claims our attention. Lodge thinks it probable that
negative and positive electricity jointly may make up the ether and
10
WIRELESS TELEGRAPHY.
that the ether may be divided into positive and negative electricity.
As an illustration of this shearing process, let A, B represent the
ether ; then, if it is sheared, as shown diagrammatically in Fig. 3, by
_ ^ p.. the dotted line dividing it into two portions, A
j t will be positive and B negative electricity. Al-
^ though Erlung asserts ether to be a perfect con-
A B ^ ductor, it is more reasonable to suppose that it
^ is a perfect non-conductor, for, according to
^ Maxwell, conductors must be opaque, while, as
• • — I 0 Lodge points out, the ether is absolutely trans-
parent.
The constants of the ether, while far from
being determined with exactness have been determined with suf-
ficient accuracy, for practical purposes. For instance, the velocity
of propagation of waves in the ether has been found to be about
168,000 miles per second.
FIG. 3. — SHEARING THE
ETHER (According
to Lodge).
CHAPTER II.
WAVE MOTION.
THEORETICAL.
In beginning the study of electric waves it is very important to
have clearly in mind the essentials of undulatory or wave motion.
Undulations may be divided into two classes (a) molecular wave
motion in gross matter imported by the impact of one molecule on
another, and (b) etheric wave motion caused by transverse vibra-
tions in the ether.
MOLECULAR UNDULATIONS.
The first principles of physics illustrate the simplest form of
wave motion of the first class in the following familiar scene.
Standing on the shore of an ocean and gazing on the gigantic waves
impelled with mighty force toward the shore, the mind is easily led
to believe that the incoming waves are carrying great masses of
water, but let a boat or a bit of wood float upon its surface and it
will be seen to rise on the wave crest and fall on the wave valley,
but making no progress in a horizontal line or toward the
shore. It is evident, then, that it is not the mass of water
that forms the actual onward movement, but that it is the particles
of water of which it is composed. These waves transmit energy
and wave motors are constructed to utilize the force so sent on
from one wave to another. Waves may travel great distances but
the motion of each particle of water is exceedingly limited.
Another illustration that gives an exceedingly clear idea of wave
motion and one that has long been in favor among physicists is the
simple wave motion shown in a rope. This idea has recently been
brought to a high degree of perfection by Dr. M. I. Pupin as an
analogue showing the constants of long electrical current waves for
long distance telephone transmission. Fig. 4 shows the undulatory
or wave motion of a rope. The distance between 1 and 2 or 3 and
11
12 WIRELESS TELEGRAPHY.
4 is termed a wave length ; 1 and 2 are the nodes or null points of
the waves caused by the crest of one wave intersecting the valley
of another wave ; the vertical distance between 3 and 6 and 4 and 5
determines the amplitude of the wave.
FIG. 4. — WAVE MOTION OF A ROPE.
Next higher in the scale are sound waves; again the cause of
sound is the molecular vibration or the impact of one molecule on
another, as a bell ringing or a whistle blowing. The vibrating
molecules of the bell or whistle impinge upon the nearest molecule
of air and these in turn pass the motion onward by impact until
they reach the ear or other receiving apparatus or until the trans-
mitted energy is lost by diffusion. Sound is thus propagated
through the air and may be transmitted through any elastic me-
dium or substance as a body of water or mercury.
The motion of air molecules is backward and forward in the
line of propagation, by longitudinal vibrations or end thrusts.
Sound, like all waves of the first class, cannot be transmitted
through a vacuum, i.e., where the air has been exhausted, and the
ether has nothing to do with its motion. Sound waves travel in
free air with the velocity of, approximately, 1,120 feet per second,
and the wave length may be found by dividing the velocity by the
number of vibrations. The particles or molecules forming sound
waves, like those of water or the rope do not travel but remain
practically stationary.
If the waves are permitted to continue only a given distance
and are then reflected back on themselves so that the line of
reflection is in the line of propagation, the wave crests and
valleys or nodal points may be easily distinguished. The waves
are then called stationary waves.
Heat offers a connecting link between the first and second
classes of wave motion, for it may be transferred from one molecule
to another like sound, while it possesses the added property of
WAVE MOTION. 13
communicating to the ether, by its vibratory atoms, waves that
travel with the velocity of light, and which are propagated by the
ether; this is called radiant heat. Eadiant heat waves differ from
those set up in the air, for ether in a space where there is no
atomic or molecular matter present, transmits waves with greater
ease than the bound ether of the air. The sun offers a good illus-
tration of the transference of radiant heat from one body to
another irrespective of the temperature of the intervening me-
dium.
TRANSVERSE VIBRATIONS.
Having now the fundamental principles of wave motion set up
by molecular impact, the next stepping-stone to electric waves is by
a familiar knowledge of the laws of light which belong to the second
class of wave motion, and these will serve to explain largely the
nature of electric waves. The only difference between luminous,
radiant heat and electric waves is a variation of the wave lengths.
Though electric and molecular undulatory motion are similar,
in that both travel in straight lines, there is yet a vast difference
between them, for in molecular matter the wave is caused by a
to and fro movement of the molecules, or by end-thrusts as at A, Fig.
5, and ether waves vibrate across the line of propagation as at B,
FIG. 5.— LONGITUDINAL IMPACT WAVE. FIG. 6. — TRANSVERSE POLARIZATION WAVE.
Fig. 6. Waves in gross matter are by longitudinal impact, those of
ether are transversal by polarization.
The history of light waves follows coincidently that of ether,
and, in fact, all other phenomena, for there were two theories ad-
vanced, both of which had their champions. The corpuscular or
emission theory found favor with Newton, who believed light to
be a form of segregated matter, each particle being smaller than the
atom and that these were projected with enormous velocity from a
body having luminous properties. Tyndall proved this theory un-
tenable by demonstrating that a body having a weight of one grain
14 WIRELESS TELEGRAPHY.
would acquire the momentum of a cannon ball traversing its course
at the rate of 1,000 feet per second, whereas the most delicate test
he could apply showed that light does not possess mechanical
force.1
Huygens advanced, in opposition to the above, the undulatory
or wave motion theory of light, and this was finally proven experi-
mentally by Young and Fresnel. Accepting now, Huygens's un-
dulatory theory and Young's transverse vibrations of light waves
and the Faraday-Maxwell electro-magnetic theory of light, that
ether waves are propagated with finite velocity, and that regard-
less of their length the velocity remains identical, we have the laws
of electric waves well within our grasp. The speed of light has
been determined by several different methods and is found to be
practically 186.500 miles per second. As early as 1676 Romer cal-
culated the velocity by the interval between two successive eclipses
of the satellites of Jupiter. Bradley devised a method by the aber-
ration of light. Fizeau measured the velocity directly in a most
convincing manner in 1849, with results closely coinciding with
Romer and Bradley. Foucault2 developed a method in 1850 de-
pending upon the Wheatstone revolving plane mirror, which had
been invented prior to that time to prove that time was required for
the spark of a disruptive discharge to take place. One of the first rea-
sons advanced for an ether was that light, however great its velocity,
required a given length of time to travel. Without entering into
a detailed description of the properties of light waves — these may
be found in any treatise on light — mention will be made of a few
of those by which Hertz was enabled to compare and so determine
the nature of his electric waves. These are reflection, refraction,
absorbtion, polarization and the final test for wave motion — inter-
ference, developed by Young in 1801 for light. Whatever is said
about light waves here may be taken, not only as analogous but as
applying directly to electric wave phenomena.
LIGHT WAVE LENGTHS.
A body emitting light produces waves of a length capable of
affecting the optic nerve, though the range of wave lengths the eye
is capable of receiving is not great, being from 271 ten-millionths
*Lebedew on Mechanical Force of Light.
2R6mer's, Bradley's, Fizeau's and Foucault's methods are fully described
in Ency. Brit.
WAVE MOTION. 15
of an inch, which is red light, to 165 ten-millionths of an inch or
violet light. This is the visible spectrum, and it is interesting to
note, in view of what has been said concerning transverse vibrations
of light, that the physiological structure of the retina of the eye, as
revealed by the microscope, is made up of minute elevations at
right angles to the surface of the retina and in the line of wave
propagation as shown in Fig. 7. To any one who has seen the
FIG. 7. — LIGHT WAVES IMPINGING ON RETINA OF THE EYE.
spectrum and given a thought to it, the idea must have occurred
as to what is above and below the visible portion, and it is true that
at both ends there are invisible waves, some being much too short
and others a great deal too long to impress the sense of sight.
Thus from some sources, especially from the electric arc and
from sunlight, a radiation or stream of waves proceeds, called ultra-
violet light, or, more properly, ultra-violet radiation, since all
waves not visible to the eye should be designated as radiations.
The wave length of the ultra-violet radiation is in the neighbor-
hood of 140 ten-millionths of an inch; the eye failing to be im-
pressed with wave lengths so exceedingly minute, recourse must be
had to something that will be' sensitive to their presence and the
action of a photographic plate answers admirably, for when ex-
posed to the spectrum it shows a color band far above that of
the violet seen by the eye; likewise will a plate record the pres-
ence of transverse waves so very short it is doubtful if they have
ever been measured correctly, although it is supposed that the
period of vibration is some 300 quadrillions per second.
So exceedingly penetrating are these transverse vibrations
that they will pass through wood, paper and sheets of metal, as
light waves pass through glass. These are the most rapid vibrations
of which we have absolute knowledge.
16
WIRELESS TELEGRAPHY.
At the opposite end of the visible spectrum are the radiant heat
waves, and these, although emitted by luminous bodies, are much
longer than the retina* of the eye is capable of sensing. From radi-
ant heat waves the length of the invisible ones gradually increases
until those are reached with which we have to deal, namely, elec-
tric waves. Light waves and other radiations have a rectilinear
motion, or travel in straight lines when propagated through a
medium of uniform composition and density, and it has been
shown that the ether absolutely fulfills these conditions.
REFLECTION. — Eeflection of light and other ether waves is simply
a change in the direction of the waves, or, in other words, the waves
are thrown back by some physical surface, usually a polished mir-
ror of metal or glass, thus changing the original direction, though
the medium through which they are propagated remains the same.
The law of reflection for ether waves is that the direction in which
the rays fall upon the reflecting surface — called the angle of inci-
FIG. 8.
ANGLES OF INCIDENCE AND REFLECTION.
FIG. 9.
WAVE FRONT GRAPHICALLY ILLUSTRATED,
dence a Fig. 8 — is exactly equal to the reflection of the waves,
called the angle of reflection b.
REFRACTION.— The refraction of light is a bending of a luminous
ray formed of waves, when it passes from one medium to another as
from air into glass. The refrac-
tion of a ray of light through
a glass prism, Fig. 9, is made
clear when it is understood that
the velocity of light is less in
glass than in air. Since ether
waves are due to transverse vi-
brations, they are therefore per-
FIG. IO.-LIGHT WAVE THROUGH PRISM. peilciicular to the wave front;
for instance, let AA represent the direction of the light or electric
WAVE MOTION. 17
/
wave, BB the transverse vibration, then the surface of the wave CC
would be the wave front. When a wave reaches the side of the
prism AB, Fig. 10, the lower end of the wave front a, strikes and
enters the glass first. This end of the wave moves more slowly in
the bound ether of the glass, while the upper end of the wave a is
still in the free ether outside the glass. The lower end of a, is so
greatly retarded in its propagation, that when the whole wave has
entered the prism, the wave front is rectified as shown at c. The
wave front being perpendicular to the path causes a change in the
direction, and the wave now travels in a straight line until the top
of the wave front strikes AC, the surface of the prism, as shown
at m. The upper end of the wave emerges first into the free,
ether and travels much more rapidly than the other end of the
front which is still impeded by the bound ether of the glass. When
the wave finally emerges from the glass as shown at n, a second
change is involved in the direction of its propagation and it is now
refracted from the perpendicular.
POLARIZATION. — Another remarkable property of light and one
with which we shall have to deal later in electric waves is polariza-
tion. Silvanus P. Thompson has offered an exceptionally clear
description of what polarization really means.1 Light from the sun
or any luminous body, he says, is non-polarized, that is, it consists of
vibrations which are not especially directed up and down, right or
left or in any given order. Natural light is not only made up of
many different wave lengths, representing so many different colors,
but it consists of waves whose transverse vibrations are all jumbled
up, that is, not polarized in any particular direction. As a me-
chanical analogue of polarization Thompson used an india-rubber
cord passing through^ a wooden box, with vertical partitions, Fig.
11 ; these partitions limit the motion of the cord and allow only the
vertical waves to pass through, irrespective of the direction of the
vibration of the cord. The waves that have passed through the box
are said to be plane polarized, i.e., all are in the same plane. If the
box is turned over on its side, Fig. 12, it will now transmit only
horizontal waves.
If a second box is used and the first one, P, is placed with its
partitions vertical, it will polarize the waves vertically, and as these,
waves reach the box marked A, also having similar partitions, the
waves will get through both boxes and are polarized in the vertical
^Thompson on "Light."
18
WIRELESS TELEGRAPHY.
plane. But if the first box, P, is set vertically, and the second box,
A, horizontally, Fig. 13, P will polarize the waves vertically, but
the box, A, called the analyzer, prevents the waves from passing
through it. However the polarizer P is placed it will polarize the
waves, but if the analyzer A is turned at right angles to P, the
waves will be cut off.
To recapitulate, when the polarizer and analyzer are parallel,
the waves — plane polarized — pass through; but when the polarizer
and analyzer are crossed, the waves are cut off. Hence by turning
round the analyzer to such a position that it cuts off the waves, the
FIGS. 11, 12, AND 13. — ANALOGUE OF WAVE MOTION.
direction of the waves emanating from the polarizer may be easily
determined. Now light and electric waves may be plane-polarized,
by means of suitable apparatus, in a similar manner to that just
described.
There is a gem, called tourmaline, which when cut into thin
slices has the property of polarizing light waves. If waves of light
are allowed to pass through a tourmaline plate it acts on them
like the polarizing box P, Figs. 11, 12 and 13, on the cord. A
tourmaline plate is shown in Fig. 14. As the waves from light
pass through the plate they are polarized.
Now if a second plate of tourmaline is
. ^= -^^/ introduced and placed in the line of direc-
FIG. 14.— TOURMALINE PLATE tion of the light waves and parallel to the
first plate, a stream of light waves will pass through both plates,
and to the unaided eye it could not be detected that the waves had
WAVE MOTION.
been polarized. Fig. 15 shows such an arrangement, with mixed
waves entering the polarizing plate P, the waves rectified after
emanating from the plate and passing through the analyzer A.
S is the source of light, and all waves entering the polarizing plate
are parallel with the axis of the plate
P ; these are readily transmitted, but
all waves in any other direction are
extinguished. The waves entering
the second tourmaline crystal A, the
vibrations of which are parallel with
its lines, pass between them and
through the crystal easily. But if
FIG. ^.-TOURMALINE PLATES. the analyzing crystal A is placed
at right angles to the polarizer P,
Fig. 16, the waves cannot pass, for the microscopic lines of the
tourmaline cut off the light vibrations and destroy the waves.
FIG. 16. — TOURMALINE PLATES.
ANALYZER AT RIGHT ANGLES TO POLARIZER.
Fio. 17. — TOURMALINE PLATES.
OPAQUE TO LIGHT WAVES.
Thus, if the crystals P and A are held before the eye as in Fig. 17,
it will appear perfectly dark, showing that no waves are passing
through. If the axes of the tourmaline crystals
are arranged at an angle of 45° the light is only
partially cut off as in Fig. 18.
These are the first principles of reflection, refrac-
tion and polarization of light and other waves in
ether, but what has been said is merely the begin-
ning, the statement having been carried only to the
CROSSED AT 45°. exten(; necessary to elucidate the experiments of
Hertz on the action of electric waves.
FIG. 18. — TOUR-
MALINE PLATES
CHAPTER III.
ELECTRIC WAVES.
HISTORICAL.
The term, electric radiation, was first employed by Hertz to
designate waves emitted by a Ley den jar or oscillator system of ^an
induction coil, and since the discovery of these radiations by that
brilliant young scientist of Karlsruhe, in 1888, they have been
called almost universally, Hertzian waves.
In this year, coincidently, Lodge investigated the theory of
the lightning rod,1 and as a necessary part of his work he made a
large number of experiments with disruptive discharges from small
Ley den jars and noted that the resultant manifestations were
electric waves in neighboring wires.
Professor Fitzgerald, of Dublin, had-, several years prior to
Hertz's discovery, theoretically demonstrated the existence of elec-
tric waves and attempted to produce them, but without practical
results. Hertz, however, had no knowledge of the work of Lodge
and Fitzgerald until after he had announced his own discoveries.
One of the nearest approaches to the discovery of electric waves in
space before Hertz, was made by Prof. Joseph Henry, of Washington,
when he succeeded, by means of a spark from a frictional machine
on an upper floor of his house, in magnetizing needles in the cellar
beneath at a distance of 30 feet with two floors and ceilings inter-
vening.2 Here were the elusive electric waves, but the knowledge
of the electro-magnetic theory of light was yet to be elucidated by
Faraday, and as Hertz pointed out, even though it had been enunci-
ated by Maxwell, this special and surprising property of the electric
spark could not have been foreseen by any theory.
Silvanus Thompson, in 1876, produced electric radiations by
an apparatus quite like the one Hertz employed twelve )^ears
later, but he failed to grasp the great underlying principle in-
20
Lightning Guards.
2Memoirs of Joseph Henry.
ELECTRIC WAVES. 21
volved — that the effects obtained were the evidence of electric waves
transversing space in exactly the same manner as light waves. The
cause of the electric waves as well as the effect produced by them
must have come under the observation of experimentalists time
and again, sometimes both together, as when Henry and Thompson
noted them, but more often the effect was observed without the
cause being suspected. As long ago as 18GG A. S. Varley, of Eng-
land, applied for a patent on a lightning bridge based on the prin-
ciple of the cohesion of carbon or metallic powder, Calzecchi-Onesta,
of Italy, observed this "coherer action" in 1885, but he attributed
it to induction.
It remained for Hertz to make known the real nature of the
phenomenon, that others before him had merely speculated upon.
Since his time the subject has been a favorite one with investigators
and has received the attention of such eminent scientists as De la
liive, Lodge, Poynting, Bjerknes, Heaviside, Poincaire, J. J. Thom-
son, Lebedew and Fleming, all of whom have contributed important
results to the accumulation of facts. The workers who have utilized
these thoughts are many, and the analyses, opinions and practical
results will be treated of in the unfolding of this and the succeeding
chapters.
EXPERIMENTAL.
When the oscillations of a disruptive discharge occur, a dis-
placement or strain in the ether in the form of a wave is produced
similar to the strain in an elastic solid. The ether resists by its
elasticity the emitted wave and when the polarizations producing it
cease, the ether resumes its normal state. To produce a wave there
must be an expenditure of energy, and the law governing the con-
servation of energy requires that the strained ether in being re-
stored shall be supplied with some other form of energy to take its
place. This law is fulfilled by the creation of magnetic flux or
lines of force in a direction at right angles to the wave. When the
magnetic lines of force disappear they give rise in their place to
electric waves, and when the waves vanish they again produce the
magnetic flux1 and so on. For this reason all ether waves are electro-
magnetic in character.
An analogue of the electric wave and its accompanying mag-
netic action and reaction may be found in the sound wave. A bell,
22
WIRELESS TELEGRAPHY.
when struck, gives rise to an elastic strain, and the strain in dis-
appearing creates velocity by setting the air particles into motion
and thus produces the strain energy in a kinetic form, by causing
another strain in the opposite direction to the first.
For the production of electric waves Hertz used a simple device,
which, according to his terminology is called an oscillator. It is
shown diagrammatically in Fig. 19 ; a a are two polished brass
FIG. 19. — HERTZ OSCILLATOR WITH INDUCTION COIL.
spheres; & &, the oscillator plates, the distance between them being
60 cm.; c c are wires connected with the terminals of the sec-
ondary of a large induction coil or other source of -high-tension
electro-motive force. As the disruptive discharge breaks through
the air gap d electric radiations in the form of waves traveling with
the finite velocity of light and all other ether waves emanate from
not only the spark, but the entire oscillator system.
The waves emitted by the oscillator system of the coil used by
Hertz were several meters in length. To detect them Hertz em-
ployed a modified form of Eeiss micrometer spark gap detector,
Fig. 20, to which he gave the name of resonator, for he found that
the best results were obtained when its natural
period of vibration was in tune or syntonized
with the oscillations and waves producing it.
The resonators Hertz employed were of several
forms, but for the first of his experiments in
electric radiations the resonator was circular with
FIG. 20^-HfeRTz RE- a diameter of 35 cm. In his earliest experiments
SONATOR. Hertz used a rectangular form of resonator. To
one side of the oscillator, he attached the resonator by a wire at a
dissymmetrical point as in Fig. 21 A, or as in Fig. 21B; when the
primary spark passes at 2, secondary sparks will also pass in the
ECTRIC WAVES.
23
gap of the resonator, but if the wire attached to the resonator is
at a point symmetrical to the spark gap, Fig. 2 1C, then no
secondary sparks will pass in the micrometer gap, though the
most vigorous primary sparking may be taking place in the
oscillator. According to Fleming this is due to the inductance of
the wire of which the resonator is composed.1 Hertz found that
FIG. 21A. — RESONATOR ATTACHED TO
OSCILLATOR AT UNSYMMETRICAL POINT.
Fi«. 2 IB. — OSCILLATOR WITH RESONATOR
ATTACHED AT UNSYMMETRICAL POINT.
without the wire connecting the resonator and oscillator secondary
sparks could still be obtained, see Fig. 2 ID, and that the energy
set in motion by the spark of the coil was propagated through space
to the resonator in the form of electro-magnetic waves. Fleming
concluded that in this case the electric displacement as he calls it,
or electric wave, on arriving at the resonator fills its spark gap and
FIG. 21C. — RESONATOR ATTACHED TO OSCIL-
LATOR AT A SYMMETRICAL POINT.
Fio. 2 ID. — OSCILLATOR WITH FREH
RESONATOR.
creates an alternating displacement and an alternating potential
difference between the terminals. When this reaches a certain
amplitude the minute air insulation breaks down and a small spark
is produced between the ball terminals of the resonator.
However this may be, it is substantially the method by which
Hertz discovered electric waves and found that they may be propa-
gated in space or guided by wires, but in either case the time con-
stant of their velocity remained unchanged. When the waves
emitted by an oscillator are transmitted through a dielectric without
the aid of guiding wires, they travel in straight lines and at right
Fleming, Journal of the Society of Arts, January, 1901.
24 WIRELESS TELEGRAPHY.
angles to the plane of the oscillator, shown by the dotted lines, Fig.
22. If the resonator / is placed in such a position that its plane
is horizontal to the oscillator plates b I, as shown, sparks will pass
in the air-gap of the resonator if it is held at proper distance
from the sparks of the oscillator where the electric waves originate,
FIG, 22. — PRODUCTION OF STATIONARY ELECTRIC WAVES.
or equal to a wave length, if measured from the point of its
greatest amplitude; g g, is a metallic plane mirror for reflecting
and producing stationary waves; now with the resonator in the
same plane but at a greater distance away, at h, hf li or h no
spark will pass in the resonator, for here the nodal points have
been reached. Hertz concluded that the length of the waves could
be determined absolutely by observing the point where the spark in
the resonator is the brightest, this being its greatest amplitude of
vibration or by noting the null points where the spark is extin-
guished. However, Sarasin and De la Rive> in 1891, ascertained
that the wave length was variable and that the nodal points changed
position, upon enlarging or reducing the size of the resonator and
that the wave length was approximately equal to four times the
diameter of the resonator.1 These investigators also ascertained
that the size of the oscillator plates affected the secondary sparks or
the position of the resonator but very little.
By placing the resonator in other planes different phenomena
are exhibited. Fig 23 shows the resonator a in a plane parallel
with the oscillator ; if the spark-gap is at the top of the resonator or
turned around until at the bottom, sparks at the oscillator will
produce secondary sparks in the gap ; but let the resonator assume
a position in which it is at right angles to the oscillator plates, as
Sarasin and De la Rive, Comptes Rendus, March, 1901.
ELECTRIC WAVES. 25
at b, then no sparks will pass, though the gap may be turned com-
pletely around.
In the original experiments conducted by Hertz a large sheet
of zinc was used for the purpose of reflecting the radiations Fig.
22, g g, and producing stationary waves which might be meas-
ured. When the sparks pass in the micrometer gap of the resonator
FIG. 23. — OSCILLATOR AND RESONATOR IN DIFFERENT PLANES.
we have an exhibition of electrical resonance, for the detector acts as
a closed circuit conductor of such dimensions that the electric waves
are propagated through it at the same rate as those emitted by the
oscillator ; when this is the case the detector is said to be in syntony
with the oscillator system, just as a tuning fork vibrating in air
and sending out waves of a given length are reproduced by a second
tuning-fork of the same size, tone and pitch as the first. After
Sarasin and De la Rive's discovery relating to the effect the size of
the resonator had upon the wave length it was believed that the
oscillator system emitted waves of many lengths, just as white light
is made up of an admixture of many wave lengths and that the
resonator responded to the wave length that was in tune with it.
Another view that gained considerable credence is that the sparking
in the micrometer gap of the resonator was not due to stationary
waves set up in space, but that the period of oscillation or wave
length corresponded to the resonator itself. However, it is now
generally accepted that the theory Hertz first advanced — that elec-
tric waves are actually present and that the resonator gives the value
of these wave lengths direct — is the correct one and the approximate
estimates the experimenter gave concerning their length, vibration
and velocity have been determined more accurately, since then and
confirm his results almost identically.
26
WIRELESS TELEGRAPHY.
In the following as well as the preceding experiments it is
assumed that the oscillator s}Tstem produces electric waves of a
given length, and thus differs from a luminous body emitting light
waves, for in the first the waves are of a single definite value and
in the second all the various wave lengths are sent forth which con-
stitute the visible spectrum and many wave lengths of the invisible
spectrum. The micrometer spark-gap resonator differs materially
from the eye as a detector of ether waves, for the organ of sight is
capable of discerning a great many short wave lengths from the
deep red to the violet of the spectrum, but the circuit of the Reiss
detector is limited to waves of a definite length like that of a
tuning fork.
To many, doubtless, there may appear to be a considerable diver-
gence in the nature of electric and light waves, but this disparity is
exactly in accordance with Maxwell's electro-magnetic theory of
A.
o
FIG. 24.— MEASUREMENT OF ELECTRIC WAVES IN A WIRE.
light; it is the frequency of vibration and length of wave that dif-
ferentiates them, making it possible for some waves to do things
which other waves cannot do. As water may be made into a
solid by freezing, a liquid at normal temperatures, or into steam
by heating, yet, after all, it is H20. So is it with ether wave
lengths; all have properties in common and each has its especial
attributes. One of the properties of electric waves is that they
travel with equal facility and velocity in open or closed -wire cir-
cuits or in space, whether the medium intervening is a dielectric
or the ether alone. The method of measurement Hertz devised
for ascertaining, the wave length in a wire is shown in Fig. 24, the
plate B is parallel with A, but is not in contact with it, the distance
ELECTRIC WAVES. 2?
may be 6 or 8 cm., and between the two may be a dielectric of
air or any other substance: from Bf a wire 1 mm. in thickness
extends to C, and then, describing a curve, the wire is carried above
the spark-gap and for some distance through the air, perpendicular
to the plane of the oscillator plates, say 15 or 20 meters. Now if
the resonator is placed in such a position that its plane includes the
wire, sparks will appear in the micrometer spark-gap and are very
bright when the detector is near the oscillator but decrease notice-
ably as the end of the wire C is reached.
Between the ends of the wire at given distances that are approxi-
mately equal, the secondary sparks decrease as the nodal points are
reached and cease sparking almost entirely when at 0; if the wire
C is cut through at a node, it does not oppose in the least the propa-
gation of the waves through it.
Another and most easily accomplished method for obtaining the
wave length in wires was used by Hertz in his analysis of the me-
chanical action of electric waves in wires. This was Herr E.
Lechers arrangement,1 and is shown in Fig. 25 ; AA1 is the oscil-
FIG. 25. — LECHER'S ARRANGEMENT OF WIRES.
lator, as described in preceding experiments. Opposite the plate,
A A1, the plates B B1 were placed at a distance of 10 cm., with
the air as a dielectric between the two sets of plates. From
B B1 two parallel wires, 6.8 meters long and 30 cm. apart extend
into space and are connected together at & b; a low vacuum tube
C — as a Geissler tube — is arranged with sliding contacts a a ; when
the tube slides over the wires it will be found to become luminous
in some portions and to remain dark in others.
Other methods have been devised, the detector consisting of a
Langley bolometer, or a Kelvin quadrant electrometer and T row-
bridge and Duane used a modified form of the Lecher scheme,
*E. Lecher, Wiedemann's Annalen, vol. 41, 1890.
WIRELESS TELEGRAPHY.
but in all cases the experiments have practically agreed and
show that the velocity of electric waves over wires is identical to
that of electric waves in space, the wires acting only as a guide for
the waves.
Knowing the method of determining experimentally the length
of electric waves and that wave propagation in ether is 186.500
miles per second/ the frequency or period of oscillation may be
found by dividing the length of the wave by the velocity in miles
per second. The greater the self-induction or electrical inertia of
a Leyden jar or oscillator system of an induction coil and the
greater the capacity of the jar or system the larger the lineal
dimensions of the wave will be. Immediately after Hertz had
proven that electrical oscillations of high frequency generated
electric waves in space he arranged the proper apparatus for con-
centrating the action and ascertaining if a further relationship
existed between the waves he had discovered and those of light.
THE HERTZ APPARATUS. — In his experiments with electric radi-
ations in free air Hertz employed a shorter wave length than 'in
those described, wherein the wave action was manifested in wires.
He used a small induction coil giving a maximum spark of
4r5<j cm. in length, but the spark-gap was cut down to 5mm. when
the tests were under way.
FIG. 26a. FIG. 26b.
HERTZ OSCILLATOR AND RESONATOR.
FIG. 26c.
WOOD FRAME SUPPORTING REFLECTORS.
The oscillator balls a a, Fig. 26&, were connected with the brass
rods b b 3 cm. in diameter and 13 cm. in length, each. These were
attached to a parabolic mirror c made of planished sheet zinc sup-
ported by a wooden framework, Fig. 26c. The oscillator system was
'There is, doubtless, a slight variation in ihe velocity of ether wave
lengths, but it is so small as to be extremely difficult of experimental
proof; for instance, it is believed that red waves of light travel slower than
other wave lengths, and the Franklin Institute has been offering a prize
for many years for conclusive experimental proof that it is so.
ELECTRIC WAVES.
29
held in place by means of four sticks of sealing wax. The termi-
nals of the coil led to the spark-gap spheres direct and the coil itself
was arranged back of the reflector. It was supplied with current
from three storage batteries.
The resonator is shown in Fig. 2Gb; it is of the open circuit
type, in contradistinction to the spark-gap resonator Hertz chiefly
employed in his earlier experiments, made in the form of a circle.
It consisted in this case of two straight pieces of wire 50cm. long
and 5mm. in diameter, separated at their ends 5cm., from which
two smaller wires at right angles with the vertical wires and
parallel to each other were arranged with a micrometer spark-gap,
formed of a brass sphere at the top and a pointed screw below. The
resonator was arranged within a parabolic reflector of similar con-
struction, to that described for the oscillator. As Hertz pointed
out in his paper on Electric Radiation,1 and Fleming by his later
apparatus has proven, there can be a considerable modification, as
to form and size, without interfering with the successful working
of the tests.
REFLECTING ELECTRIC WAVES. — By placing the concave, para-
bolic zinc reflectors back of the oscillator system and resonator,
FIG. 27. — SOUND AUGMENTATION BY RESONANCE.
having the axis of their oscillators in the focal line of the mirrors,
it was found that there is no manifestation behind or on either side
of the mirrors. Here we have an example of a shadow cast by the
electric wave. When the mirrors were placed so that their apertures
face each other, as in Figs. 26, the waves were reflected from the
polished surface and were found to reinforce the advancing waves
like the condensation of air between two tuning forks, as in Fig. 27.
At other points again the two sets of waves weaken one another
like the rarefaction of sound waves as indicated in Fig. 28; in
this way the nodal points and wave crests may be distinguished
lWiedemann's Annulen, vol. 36, p. 769.
30 WIRELESS TELEGRAPHY.
easily. Again, if the detector and oscillator reflectors are arranged
as shown at Fig. 29, A and 5, no sparks will pass in the resonator
FIG. 28. — RAREFACTION OF SOUND BY INTERFERENCE.
until the plane sheet of metal C is set in such a position that the
right angle was obtained to re-
flect the waves from the oscil-
lator into the aperture of the re-
ceiving mirror, and a variation
of this angle was sufficient to
change the direction of the waves,
and thereby cause the sparks to
FIG. 29. — REFLECTING ELECTRIC WAVES, j • TJY^POT.
' RECTILINEAR PROPAGATION. — Among the many tests Hertz ap-
plied to demonstrate that electric waves travel in straight lines,
one was to place a sheet of zinc between the oscillator and resonator
in the position shown in Fig. 29, or between the two mirrors. With
the plane sheet of metal in place the sparks in the resonator dis-
appear, or if a person crosses the path of the waves the sparking
ceases in the detector spark-gap, showing that the waves were
intercepted. Electric waves pass through all insulators and are
intercepted by all conductors except in the case of liquids, which
conduct in virtue of their electrolytic properties, but otherwise
follow the law of insulators, all this being in accordance with Max-
well's fundamental law.
REFRACTION. — To ascertain if the electric waves were refracted
when they pass from the air into another insulating medium, Hertz
constructed a huge prism by chipping a cube of pitch until the de-
sired angles were obtained. This pitch prism had a refracting
angle of 30° and by its use the experimenter was able to discern a
refraction of 22°. With Fleming's apparatus1 it is quite easy to
exhibit the power of insulators to refract the waves with a prism of
Fleming, on Electric Waves, Journal of the Society of Arts, January
18, 1901.
ELECTRIC WAVES.
31
much smaller dimensions than Hertz used. Fleming's apparatus
consists of two metal boxes, Fig. 30, placed with their open ends to-
wards each other and about 50cm. apart. At A, Fig. 30, is the
oscillator. The boxes are made of sheet zinc.1 From the sides of the
Fio. 30. — REFRACTION OF ELECTRIC WAVES.
box protrude zinc tubes and inside of these are ebonite or other
insulating tubes, containing brass rods 8 or 10cm. in length and
terminating in brass balls forming the spark-gap; the balls are
adjusted to give a spark 1mm. in length. To the opposite ends of
the brass rods are long spirals2 of gutta-percha covered wire filling
up the rest of the tube. The outer ends of these spirals are con-
nected with the secondary terminals of the induction coil; when
the apparatus is in operation sparks pass between the oscillator balls,
and the electric waves resulting emanate from the aperture of the
box.
The box containing the detector is exactly like the one described
containing the oscillator system; instead of the resonator Hertz
employed, Fleming uses a later product of science, a coherer of
simple form, with nickel filings. The coherer is inside the receiving
zinc box and the wires connecting with it are brought out through
a metal tubing, this precaution being necessary to prevent extraneous
waves from manifesting themselves therein. This tube with the
inner insulating conductor leads to another metal box containing a
bell, relay and battery, as in the ordinary wireless signal apparatus
described in a later chapter.
Now if the emitting and jeceiving boxes are set up with their
*Zinc is usually employed because it is very much cheaper than copper,
and is not magnetic, as sheet tin (iron) would be.
2 The object of the spirals is to increase the self-inductance of the os-
cillator system.
32
WIRELESS TELEGRAPHY.
apertures at such an angle that the electric waves emerging from
the oscillator system do not .pass into the aperture of the receiv-
ing box, the detector system is not affected, but on introducing a
prism of pitch, glass, wood or paraffin, so that it is in the path of
the electric waves, it is bent out of its course and is refracted into
the opening of the receiving box. The object in using paraffin or
pitch for the prisms is that the length of the waves under in-
vestigation being greater than where light is used, a much larger
prism is needed than may be readily obtained in glass. Any in-
sulating substance having a homogeneous structure may be used
with equal advantage. Fleming has concentrated the electric waves
by means of a piano-cylindrical lens of paraffin. The apparatus
may also be used in all the experiments made by Hertz in which he
employed the large zinc reflectors.
POLARIZATION. — Hertz sought for and found a method to ascer-
tain if electric waves consisted of transverse vibrations like light.
This he did by polarization. IJe arranged the mirror Af Fig. 31,
FIG. 31. — POLARIZING ELECTRIC WAVES.
with the enclosed detector so that it could be revolved about
the axis of the electric ray ft &; both the resonator C and the
mirror A were in the horizontal plane to the emitter D and the
mirror B; when the foci A and B are at right angles to each other
the mirrors perform the same functions as an
optical polarizer and anatyzer, or the crystals of
tourmaline or the boxes with the partitions of-
fered as an analogue for polarization. Another
mode of polarizing the electric wave, and a close
counterpart to the Thompson rope analogue, is
by means of a wooden frame with parallel wires
WAVES. arranged 3cm. apart, Fig. 32.
If this screen is interposed with the wires perpendicular to the
FIG. 32.— POLARIZER
ELECTRIC WAVES.
J(
J
FIG. 34. — POLARIZER AT RIGHT ANGLES
TO WAVE FRONT.
-electric ray, as in Fig. 33, the waves pass and produce a spark in
the detector, but if the screen
is set up so that the wires will
be at right angles to the wave
front, the ray is stoppedrcom-
pletely, as at Fig. 34.
If the receiving mirror is
again placed as at Fig. 31,
FIG. 33.-PLANE POLARIZED WAVES. and the wire screen inclined
at an angle of 45° to the horizontal, then sparks may be seen in
the detector. Here, then, is another and most striking similarity
between the action of light and electric waves. Electric waves
may be of any length from 10,000
miles, produced by the lightning
flash and having a period of ap-
proximately 18 oscillations per
second, down through radiant
heat, the visible spectrum, to the
invisible ultra - violet radiation,
having a wave length of 185 ten
millionths of an inch with 1500 trillion oscillations or vibrations
per second.
Lebedew and Fleming have produced electric waves so short
as to be measured by the ten-millionths part of an inch; so short
they could be seen, in fact, they were light waves, and reversed, light
waves are, as we know, electro-magnetic waves.
In all the experiments cited the production of the electric waves
was due to the surging of electric oscillations through the oscillator
system seeking to find its potential level, and this was caused by the
disruptive discharge breaking down the air-gap.
FREE ELECTRIC AND SLIDING HALF-WAVES. — To account for
the phenomena of electric wave propagation over great distances
where the curvature of the earth intervenes between the oscillator
and resonator, two theories have been advanced. The first is that
of the rectilinear propagation of free electric waves and the second
is that of sliding half -waves.
Blondel,1 Taylor2 and Fessenden3 have evolved the sliding half-
'Syntomy in Wireless Telegraphy. Archives, Academy of Sciences
Aug. 16, 1898. Blondel.
2 London Electrical Review, May 12, 19, 1899. Taylor.
3 Transactions Am. Inst. Elec. Engs., Nov. 1889. See also Fessenden's
work in Wireless Telegraphy; Collins; Elec. World and Eng. Sept. 19, 1903.
34 WIRELESS TELEGRAPHY.
wave theory which, briefly described, is as follows : In wireless teleg-
raphy, where the oscillator and resonator^ systems have earthed
terminals and high aerial wires, the spark-gap is located very closely
to the surface of the earth, as shown in Fig. 35. It is contended
FIG. 35. — PROPAGATION OF SLIDING HALF-WAVES.
that the vertical wire of such an oscillator is the only portion of
it capable of emitting electric waves, in which case they must of
necessity be in the nature of half -waves, since the earthed arm of
the oscillator is so short when compared with the opposite or
aerial arm that it is of little consequence. Under these conditions
the lower half of the wave would be represented as a reflection or
an image shown by the dotted lines. These half-waves being de-
tached, slide over the surface of the earth with the wave front per-
pendicular to its surface. The half-waves sliding over the surface-
of the water or earth follow its contour, just as electric waves
follow a bent wire, so that it matters but little whether or not the
sending and receiving stations are in a direct visual line.
The author has held to the theory of free electric wave propaga-
tion, since there is no experimental proof that a spherical electric
wave can be divided and maintain its integrity or an electric wave
can be formed so that one-half of it is real and the other half
imaginary. In the free electric wave theory, it is assumed that
spherical waves, like light waves, are emitted and these on reaching
the higher strata of rare-
fied air, which becomes
a conductor of current
electricity, and also a
non-conductor of electric
waves are then reflected,
as indicated in the dia-
gram, Fig. 36, when the
Fio. 36.— PROPAGATION OF FREE ELECTRIC WAVES, radiations impinge On the
ELECTRIC WAVES. 35
resonator system of the receiver. Where the distance between the
sending and receiving stations is not great and the instruments are
in a direct visual line with each other as A B, the action is of course
direct and without the losses due to diffusion and absorption. The
former theory of sliding waves, minus that dealing with half-waves,
is based upon Hertz's deductions as set forth in his paper on "Pro-
pagation of Electric Waves by Means of Wires/' 1 and the latter
theory upon his investigations of free electric waves as described in
his paper on "Electric Kadiation." 2
'Hertz, Electric Waves. Trans, by Jones.
'Hertz, Electric Waves.
CHAPTEE IV.
DISRUPTIVE DISCHARGE.
HISTORICAL.
The phenomenon of an electric spark springing across an air-
gap, or a disruptive discharge, was probably the first electrical dis-
turbance witnessed by man to which he gave a thought. When the
Traustralian of the Post-Glacial Age saw the terrific zigzag light-
ning shattering the air in discharging from a cloud to the earth or
to another cloud he sought shelter within his cave and thought long
and hard, within the limits of his ability. But he wrestled with
the subject in vain.
That was half a million years ago at least, and the query orig-
inating in the brain of this prehistoric being was not answered
until Franklin established the electrical nature of the display, and
therefore its identity, when he flew his kite in 1750 in Philadelphia.
The disruptive discharge had been produced and noted as early
as 1602 by von Guericke, and by Newton in 1643, and again by
Hawksbee in 1705, but the sparks they observed were so minute as
to be barely visible to the unaided eye, and as they appeared to be
of the same origin as heat, the name of electrical fire was given to
them. During the succeeding forty years many other experimenters
produced and witnessed the sparks as they restored the electrical
equilibrium of the charged objects, but nothing more was added
of importance to the knowledge until the invention in Leyden,
Germany, in 1745, of a jar or phial whereby the electricity could be
accumulated and preserved in considerable quantities. This served
to stimulate interest in the study of electricity in general and of
the disruptive discharge in particular. 'To whom the honor is due
of inventing the Leyden jar is not known with certainty, but it has
for its claimants three distinguished investigators of that period;
these were Kleist, a monk, Cuneus, a philosopher, and Musschen
broek, a professor.
To Sir William Watson, however, as much credit is due as to
36
DISRUPTIVE DISCHARGE. 37
the original inventor, for it was he who conceived the idea of
coating the inner and outer surfaces of the Ley den jar with tin-
foil as well as to be the first to observe the spark upon its dis-
charge.
Allemand, of Leyden, and Franklin were the first to explain
the action of the spark and the jar as an accumulator of elec-
tricity. For nearly another century the observers of disruptive
discharges were confined to electrostatic sparks produced by fric-
tional machines and jars, in fact, until a new and better way was
opened by Faraday's discovery of the induction of electric currents
in 1831. This led to the modern induction coil, brought to such a
high degree of perfection by Ruhmkorff, of Germany, in 1850; it
was now possible to obtain a continuous series of disruptive dis-
charges between the secondary terminals. In the next few years
the striking or explosive distance, as the distance through which the
spark passes in a dielectric is termed, was greatly increased and a
coil constructed by Mr. Apps, of England, for Mr. Spottiswoode,
gave a spark 42 inches in length, the longest on record for many
years.
While the instrument makers were devising more efficient ap-
paratus for the production of disruptive discharges the scien-
tists were engaged in examining their nature. In 1842 Joseph
Henry suggested that the spark was not a unit in itself but that
each spark consisted of a number of minute sparks ; in 1850 Lord
Kelvin mathematically demonstrated it, and in 1859 Fedderson
experimentally proved it by analyzing it with a revolving mirror.
While improvements were in order during the next twenty years,
the striking distance of the Spottiswoode coil had not been dupli-
cated, the limit having seemingly been reached. Elihu Thomson,
in 1877, produced, by means of a high frequency apparatus invented
by him, sparks 64 inches in length.
In 1880 Trowbridge succeeded in obtaining disruptive dis-
charges measuring 7 feet in length, and these spark lengths were
later eclipsed by Tesla, with a similar high frequency, high-poten-
tial discharge1 of an explosive length so great that the word spark
became a misnomer when applied to it ; it was in fact a miniature
bolt, resembling in every particular the tortuous path of ramified
lightning.
^Tesla Lecture before the American Institute of Electrical Engineers.
38
WIRELESS TELEGRAPHY.
PHYSICAL.
The simplest method for obtaining a disruptive discharge is
by means of the electrophorus, an electrostatic induction apparatus.
After the hard-rubber plate A, Fig. 37, is charged by a brisk rub-
bing with a piece of flannel or cat's skin,
the metal disc B is touched with the finger
causing the — electricity to be dissipated
and the cover or disc B to be charged with
4- electricity. On the disc being lifted
and the knuckle presented, as shown, the
difference of potential will be sufficient to
cause the breaking down of the air-gap
and consequently the passing of the spark.
Frictional electric and other plate ma-
chines follow practically a similar course
in charging and discharging, but to retain
or store the electricity recourse must be
had to the Leyden jar. To discharge the
jar the finger or other negatively electrified
body may be brought closely to or in contact with it. The
physiological effect of a discharge, even from a small jar, is a
"shock," and, if sufficiently intense, is painful ; in cases where the
heart is weak it is dangerous. To avoid
the unpleasant sensation described, a
discharger, Fig. 38, is employed. It
usually consists of two pieces of brass
wire, hinged together with a pair of
insulated handles and the terminals FlG- 38.— DISCHARGER.
fitted with brass spheres of small diameter. The outer coating of
tinfoil should be in contact with one arm of the discharger first.
FIG. 37. — ELECTROPHORUS.
FORMS OF DISCHARGES.
There are many different forms of discharge between the ter-
minals of a jar or induction coil, and with the increase in frequency
and potential there is a corresponding increase in variety. The
three principal ones are the disruptive, convective, and conduc-
tive discharge. The convective discharge may be seen glowing
from the positive terminal of a frictional machine or an induction
DISRUPTIVE DISCHARGE. 39
coil, and is caused by the electrification of the air particles, which
on being charged are projected by repulsion into the surrounding
space, still carrying the charge; in Geissler tubes and other tubes
containing residual atmosphere, as the low vacuum Crookes tube,
the convective discharge is easily produced and may be closely fol-
lowed. When a wire joins the opposite terminals of a jar or coil
and the potentials are equalized by discharging the current through
it, a conductive discharge results, the phenomenon being identical
to the discharge through a wire from one terminal of a battery to
the other. When the potential difference is great enough to break
down the air, or other dielectric separating the terminals, a surging
takes place through the insulating medium before it is restored, the
visible effect of which is manifested in the spark. This is the
disruptive discharge and is the most suitable discharge for the
emission of electric waves.
The initial energy of the disruptive discharge depends on at
least four factors, and according to Jaumann upon five. The first
and most important of these is, of. course, the potential at the
electrodes or terminals of the secondary coil, and these usually
consist of metal spheres, Fig. 39; in wireless telegraph practice
these spherical electrodes are called
the oscillator l)alls. If the poten-
tial difference is sufficiently diver-
gent and the quantity of induced FlG- SQ.-USUAL FORM OP SPARK-GAP.
'current great enough, the spark is so intense that it will disrupt
the dielectric placed between. the terminals. A charge is often so
excessive in a Leyden jar that the mechanical strain of the glass
separating the coatings of tinfoil causes it to give way and the
discharge piercing it breaks the vessel. With a 9 or 10 inch heavy
spark from a coil, cubes of glass three inches in thickness are easily
shattered.
DISCHARGE THROUGH DIELECTRICS.
Disruptive discharges through fluid and solid dielectrics, as oils
and glass, have been tested, with the object of increasing their wave
emitting properties, but while the break is more sudden, there is a
corresponding decrease of energy available for sending out the
electro-magnetic waves; at the present time nearly, if not all, the
best wireless telegraph systems are using the air as a dielectric, for,
•10 WIRELESS TELEGRAPHY.
as Lodge clearly puts it, the air constitutes a self -mending partition
and upon the passage of every spark it is instantaneously as good
as new again. This holds good for oil, which has been used, and is
now occasionally, for it does offer a higher insulation than does
air, before the break, but this good feature is largely counteracted
by the greater resistance offered during the passage of the spark.
What the exact resistance of oil, air or other dielectric is at the
moment of disruption is not known, but in any case, the value
cannot be great. One good feature of the oil dielectric is that it
effectually prevents the oscillator balls from tarnishing. In Fig.
40 is shown a spark-gap formed in a dielectric of oil. When a
spark takes place in oil it is of a
greenish-white color. Bisulphide of
carbon and spirits of turpentine are
excellent liquid dielectrics, and in
these the spark is very bright; in
=
^
40.-SPABK-GAP FOBMED OF Oil, ^^ ^ fc ^ . by gubmerging ^
oscillator balls in water and having a very short striking distance,
the spark may be had with little difficulty.
COLOR, SIZE AND SHAPE OF DISCHARGES.
The best practical guide to the working efficiency of a wireless
telegraph transmitter is by making careful observations of the
color, size, shape and sound of the disruptive discharge. To deter-
mine the effect of the disruptive discharge on the air, de Nikolarene
arranged between two ebonite rings a layer of cotton-wool, and this
he placed in the path of the spark; after discharging through it
the cotton-wool was found to be compressed on either side forming
a canal 6mm. wide.1 The explosive effect of a disruptive discharge
is of electro-static origin rather than due to heat ; with a large
coil provided with an ordinary mechanical interrupter the spark is
brilliant in color, zigzag in form, and produces a sharp crackling
sound, but if the induction coil is equipped with an electrolytic
interrupter of the Wehnelt type or a mercurial turbine interrupter
the discharge loses these characteristics and presents instead an
arc, less brilliant in color and giving forth a hissing sound. The
second factor on which the effectiveness or inefficiency of an elec-
tric wave emitter depends, relates to the form and dimensions of the
^Journal de Physique, August, 1899.
DISRUPTIVE DISCHARGE.
41
terminals or oscillator balls. Where two points are employed,
as in Fig. 41a, and are separated just beyond the striking dis-
tance, a luminous convective discharge, called a brush discharge,
takes place from the positive terminal especially, and if the points
are so adjusted that an occasional spark will pass, the brush will
be seen to act as a path for the latent sparks. While streams of
electrified air precede the disruptive discharge in any case, yet
where it is so pronounced as to be visible it detracts largely from
its wave emitting qualities, probably by a lowering of the specific
resistance of the air.
Where a point and a disk b, Fig. 41, form the terminals of the
air-gap the brush discharge is brighter than with two points, and
Fio. 41a. — SPARK-GAP WITH POINTED ELECTRODES.
FIG. 416. — SPARK-GAP WITH POINT AND DISK.
unless the normal striking distance is considerably cut down the
disruptive discharge is quite difficult to obtain. With a point and
a sphere, c, Fig. 41, the brush loses its visible properties where
small coils are used and is faintly luminous with larger coils, but
Fio. 41c.— SPARK-GAP WITH POINT AND BALL.
FIG. 41d.— SPARK-GAP BETWEEN Discs.
the disruptive discharge is persistent. With two disks, d, Fig. 41,
there is a convective discharge around the periphery of each unless
they are carefully rounded, and, when the sparking distance is at its
maximum, the disruptive discharges constantly shift from one
position to another. From these facts it is clear that to obtain the
best results the terminals or electrodes should offer no sharp edges
or points to assist a convective discharge, and so spheres of melal
are the usual form, the disruptive discharge breaking down
the air-gaps between the peripheral portions offering the shortest
striking distance. It was believed, until quite recently, that the
length of the electric waves depended largely upon the size of the
electrodes or oscillator balls, but it has since been determined that
the wave lengths vary with the inductance and capacity of the
42 WIRELESS TELEGRAPHY.
oscillator system, and that the length of the waves is influenced
by the oscillator spheres only in so far as their size alters the
capacity of the system.
After what has been said, it is self-evident that the spark depends
largely upon the distance between the oscillator balls or terminals.
When the striking distance represents the maximum capacity of the
coil the sparks are long, ribbon-like, and attenuated, as shown in
Fig. 42, which is a photograph of a 42-inch spark, from a meter
FIG. 42. — 42-iNCH SPARK.
spark coil made by Queen & Co., for the Japanese government for
cableless telegraphic communication between Corea and Japan.
When the air-gap is cut down to 32 inches, the spark passes between
the terminals in the form of a pencil of light of gigantic propor-
tions, Fig. 43, with a wavy luminous effect, giving forth a blue
blaze of electrical energy and capable of emitting waves of great
penetrative power.
STRIKING DISTANCE.
It is necessary, in order to obtain the greatest efficiency in the
production of electric waves, to cut down the length of the spark-
gap until the striking distance is approximately forty times less
than the maximum distance through which the disruptive discharge
takes place:1 this, in the case of the 42-inch spark, would give a
working value of lA inch, or, with a standard 10-inch coil, a
working spark of one-quarter inch. This ratio varies with the fre-
quency and potential of different coils, and in very small coils
the discharge may give the best results when the terminals are
separated one-tenth of the total striking distance. The heavy dis-
ruptive discharge shown in Fig. 43 is termed usually a "fat" spark,
and a good heavy spark is the first requirement for the wireless
transmission of intelligence.
1 This refers only to the usual high tension induction coil.
DISRUPTIVE DISCHARGE.
43
The fourth factor in the initiation of the disruptive discharge
•depends on the nature, pressure and temperature of the gas or
medium in which the spark takes place and need not be discussed
FIG. 43.— 32-iNCH
"here, since, as has been pointed out, air and oil furnish the best
practical dielectric for the spark-gap.
I A clever device invented
6-\ by Fessenden, the purpose of
which is to maintain a cer-
tain definite relation between
the inductance, capacity and
resistance without regard to
the potential employed, is
shown in Fig. 44. The dis-
ruptive discharge takes place in
air under pressure, the spark
being formed in the gap be-
tween the point 4 and the
plate 5. In using this appar-
atus the terminals are adjusted
to about one-quarter of an inch
apart when using a 12-inch
coil. By increasing the pres-
sure the dielectric strength of
the air is increased and the
spark-potential can be raised to almost any amount without any
material loss in the power of the oscillator, as indicated by the
line a, Fig. 45, whereas in air under ordinary pressure it is found
FIG. 44. — COMPRESSED AIR SPARK-GAP.
44
WIRELESS TELEGRAPHY.
Fio. 45. — SPARK POTENTIAL CURVE.
that no matter how high the potential is raised,practically no in-
crease in efficiency is obtained higher than is given with a spark
length, as indicated by the line b. The horizontal line c indicates
the potential of the spark in
inches, and the vertical line d
represents the radiation.
In relation to Jaumann's as-
sertion, that the spark is affected
by a variation of the magnetic
field, it will be omitted, as his
theory is not sufficiently estab-
lished to assist in any way the
improvement in the working qualities of the spark.
ACTION OF ULTRA-VIOLET LIGHT.
The curious observation that the disruptive discharge of one
induction coil possesses the property of increasing the length of
the spark of a second induction coil was made by Hertz, who traced
the phenomenon through a long series of splendid experiments and
finally determined that it was caused by the ultra-violet radiation
falling on one of the oscillator spheres. In these investigations
Hertz * found that the electric spark itself was richest in emitting
the invisible ultra-violet rays, but that the flame of a candle if held
near one terminal of the spark-gap was sufficiently productive to
cause sparking when the striking distance was otherwise too great
to permit the spark to pass.
The apparatus employed by
Hertz in his photo-electric re-
searches is illustrated in Fig. 46.
An ordinary induction coil A is
connected with the oscillator sys-
tem 5; a second and smaller in-
duction coil C having a very small
spark-gap at D was set in a plane
parallel with the larger coil, so
that the emitted waves from both
oscillators will receive the waves.
The primaries of both coils were
46. connected in series with a com-
mon source of E. M. F., and with an interrupter / common to both
lWiedemanri's Annalen, vol. 31.
DISRUPTIVE DISCHARGE. 45
coils. When the spark-gap B was screened from that of D by a
sheet of glass, the sparks discharging across the latter became very
much smaller and this effect led Hertz to conclude that it was not
the visible waves of light that produced this property, but the ex-
tremely rapid invisible ultra-violet waves.
The electric arc light is, next to the disruptive discharge, the
most effective method of producing sparks or increasing them.
Hertz states that if the oscillator balls are drawn so far apart that
sparks cannot pass and an arc light is started at a distance of from
1 to 4 meters, the sparks begin to pass and cease when the arc
light is cut out. By means of an aperture held in front of the arc
light he was enabled to separate the ultra-violet radiation from the
visible luminous rays of the glowing carbons, and found that the
ultra-violet radiation was the direct cause.
In wireless telegraphy any cause having a tendency to ab-
normally increase the length of the spark, likewise decreases the
efficiency of the electric wave emitting system, and, therefore, the
ultra-violet radiation falling upon the oscillator balls is detri-
mental to the proper working of the apparatus. Lodge has secured
patents in the United States and England for excluding these
radiations, which he does by means of colored glass encasing the
oscillator balls.
Sparks of an irregular form may be traced to an uneven dis-
tribution of the metal vapor from the electrodes, and is caused
largely by unclean terminals; the oscillator balls should be kept
perfectly clean and should be polished frequently. Since the dis-
ruptive discharge is electrolytic in character, different metals have
been tested with a view of ascertaining the most consistent ter-
minals ; spheres of copper and aluminium have been found to yield
the best results, although brass terminals are almost universally
employed.
DIRECT AND ALTERNATING CURRENT EFFECTS.
An intermittent arc formed between metals resulting from the
break of contact either by a direct or alternating current suffices to
produce electric waves of considerable intensity, and if in the prox-
imity of a sensitive coherer will affect it. While conducting some
experiments in New York City, the author had to contend with the
sparking of a trolley as it passed an uneven juncture in the con-
ductor. Although the distance was nearly one hundred feet, yet
46 WIRELESS TELEGRAPHY.
every spark cohered the filings. Another source of trouble from
extraneous sparking by direct currents is due to the relay and tapper
contacts breaking the battery circuits of the receiving devices. The
remedy for these untoward effects is the employment of choking
coils. To test the striking distance best adapted for a given coil
as an electric wave emitter, a Eeiss micrometer spark-gap detector
is the most convenient. By setting the detector and radiator or
oscillator system in the same horizontal plane and observing the
secondary sparks while adjusting the oscillator balls, the brightness
of the detector sparks as well as their length will be found to
indicate clearly when the maximum value of spark-length has been
obtained. .With a disruptive discharge of the proper density and
length, powerful oscillations may be easily set up in an open circuit
radiator and electric waves capable of intense penetration traversing
long distances may be produced.
CHAPTER V.
ELECTRIC OSCILLATIONS.
HISTORICAL.
In the historical retrospect of electric oscillations two classes
are observed: (1) that of commercial low frequency alternating
currents produced by moving coils of wire in a magnetic field, and
(2) the surging of high frequency, high potential currents through
a low resistance as the oscillator system of a coil or jar.
In Gilbert's Annalen der Physilc, published in 1806, the phe-
nomenon of the "back-stroke" in lightning discharges is spoken of
as a common occurrence. But the first suggestion that the dis-
ruptive discharge was caused by the to and fro motion of the
electric current was distinctly expressed by Felix Savart, of France,
who was perplexed by the irregularity of the magnetization in small
needles when affected by the discharge of a Leyden jar.1
Joseph Henry contributed a paper to the Philosophical Society
in June, 1842, on his investigations of some anomalies in ordinary
electrical induction. He repeated Savart's experiments with No. 3
and 4 sewing needles, subjecting them to a magnetizing helix, and
found the polarity always conformable to the direction of the dis-
charge and that when very fine needles were employed an increase in
the force of the electricity produced changes in polarity. This
puzzling phenomenon was finally cleared up by the important dis-
covery that an electrical equilibrium was not instantaneously
effected by the spark, but that it was attained only after several
oscillations of the current.
Henry himself says: "The discharge is not correctly repre-
sented by the single transfer from one side of the jar to the other ;
we must admit the existence of a principal discharge in one direc-
tion and then several reflex actions backward and forward, each
more feeble than the preceding, until the equilibrium is ob-
tained." 2
Edinburgh Journal of Science, October, 1826.
'Proceedings American Philosophical Society, June, 1842.
47
48 WIRELESS TELEGRAPHY.
Five years later, in 1847, Helmholtz communicated his views,,
which were evidently independent of those of Henry. In his paper,
Ueber die ErJialtung der Kraft, Helmholtz suggested the electric
oscillations and said he assumed the discharge of a jar not a simple
motion of electricity in one direction, but a backward and forward
motion between the coatings of oscillations which become con-
tinually smaller until the entire vis viva is destroyed by the sum
of the resistances,1 and again, five years later (in 1852), Lord
Kelvin, deduced the phenomenon mathematically, the results coin-
ciding almost exactly with Savart, Henry and Helmholtz. Faraday
arrived at the same conclusion experimentally by decomposing water
with an ordinary f rictional electric machine, and showed that hydro-
gen and oxygen rose in a mixed condition from either electrode, and
that this was due to electric oscillations of the discharge. In 1859
Fedderson proved the oscillatory nature of the electric discharge
by observing the spark in a Wheatstone revolving mirror, as first
suggested by Lord Kelvin. Photographic proof of the oscillations
has not been wanting in recent years. Yernon Boys, in 1890,2
made some exceedingly fine photographs of the principal and
supplementary sparks of the discharge, each of which left a well-
defined and separate record on the negative. Trowbridge obtained
photographic proof that the long seven-foot sparks were oscillatory.
Some very interesting photographs of electric oscillations have
been made by Dr. E. W. Marchant with a revolving mirror, with
and without iron cores in the coils. Many facts have been added
within the past two years, and the laws governing the emission
of electric waves are, for the most part, quite well known.
PRACTICAL.
Low FREQUENCY CURRENTS. — In commercial alternating cur-
rent generators the current flow reverses direction from 50 to 300
times per second. By increasing the number of polar projections
or the speed of the armature, or both, a higher frequency may be
obtained, but the limit is soon reached. In telephone circuits the
frequency of reversal may be 1,000 or more per second. These are
simple periodic currents having characteristic curves. A low fre-
Scientific Memoirs of Helmholtz: edited bv Tyndall, 1853.
^Proceedings Physical Society, London. 1890.
ELECTRICAL OSCILLATIONS. 49
quency alternating current requires the element of time for the
maximum positive to change to the maximum negative potential,
and vice versa; the e. in. f.
and current strength are kept
at a constant value by the
generator, hence the constants
usually follow some smooth
Curve, as in Fig. 47. FIG. 47. — ALTERNATING CURRENT CURVE.
HIGH FREQUENCY CURRENTS. — To obtain electric waves an
alternating current of exceedingly high frequency having a period
of reversal many times greater than can be produced by mechani-
cal means must be employed. There is but one method known to
science by which electric oscillations of the requisite frequency for
the emission of electric waves may be had. This is by discharging
a condenser or oscillator system through a circuit of small resistance
and allowing the maximum positive and negative charges to restore
the electrical equilibrium through a disruptive discharge, this
forming at the moment the spark passes a conductor of low re-
sistance, there is then set up in the oscillator system high fre-
quency currents, the duration of which may be measured by the
ten and hundred thousandths part of a second. In this case depend-
ing on the capacity, inductance and resistance of the circuit the cur-
rent will oscillate to and fro several times before it is finally damped
out by the sum of the resistances.
Alternating and oscillating currents, of whatever frequency,
are governed by the electrical dimensions of the oscillator system,
and these factors, i.e., ohmic resistance, inductance, and electro-
static capacity, all tend to slow down the frequency. Ohm's law
does not apply to the circuit, but its value largely depends on
the frequency with which the reversals take place, and, in circuits
containing iron upon the e. m. f. By increasing the frequency of
the current the ohmic resistance decreases in value while the in-
ductance and capacity increases. In oscillator systems where high-
frequency currents are induced by a disruptive discharge the effect
of resistance is usually so small as to be negligible.
ANALOGUE OF ELECTRIC OSCILLATIONS. — A mechanical ana-
logue, designed by Fleming,1 illustrates the electric action taking
place in an oscillator system at the moment of discharge; it is
shown in Fig. 48. It consists of a glass tube bent in the forpi of
Fleming, Cantor Lecture, Jan., 1901, Society of Arts, London.
50
WIRELESS TELEGRAPHY.
a U ; it is partially filled with mercury, which is so displaced that
there is a difference of level between the parallel tubes a and b;
gravitational force is therefore exerted upon the two columns of
mercury, tending to cause the high and low levels to equalize. If
this force is allowed to act slowly the mercury will find its normal
level, without oscillation. But if
the force is allowed to act sud-
denly, the mercury, in virtue of
its density, flows beyond the nor-
mal level, indicated by the dotted
line, and then returns, its inertia
causing several oscillations of the
fluid metal before coming to rest.
If the tube is rough inside, the
mary friction offered to the mercury
Positive
x v>
Secondary
Negative
98
FIG. 48.-ANAix>Qt,» OF ELECTRIC OSCIL-
I'ATION8-
has a damping effect and permits
only one or two oscillations to
take Place 5 in electric OScilla'
tions the inductance of the sys-
tem has the effect of slowing down the oscillations. The resistance
offered to the flow of the mercury by the abrased surface of the tube,
or in other words, the friction, corresponds to the ohmic resistance
of the circuit; the denser the liquid in the tube the less appreciable
will be the effect of the friction, likewise the higher frequency
of the discharge the less the ohmic resistance of the circuit affects
the oscillations.
If the glass tube contains air above the mercury and the ends
are hermetically sealed, the air will be compressed by the impact
of the mercury and acts similarly to the electrical capacity of the
oscillator system. It is evident that to produce oscillations in a
mechanical body, as mercury in the U-tube system, the first requisite
is that of density, so that when the mercury is displaced it will tend
to return to the level from which it started and will oscillate to and
fro in accordance with this tendency. For obtaining the best re-
sults in electric oscillations the system must be composed of metal-
lic bodies having electrical capacity and the system must have the
coefficient of inductance and possess low resistance.
PROPERTIES OF ELECTRIC OSCILLATIONS. — The frequency of
oscillation attained by a high potential current through the dis-
ELECTRICAL OSCILLATIONS. 51
ruptive discharge of a Leyden jar may range approximately from
1,000.000 to 10,000,000 per second. The decadent reversals in
oscillator systems may be ten times less than in the case of the jar.
By properly arranging the capacity and inductance of a system
the number rate may be as slow or as rapid as desired, depending,
as we have seen, on the coefficients of the circuit, i.e., capacity,
inductance and resistance. The number of complete oscillations or
swings for each initial discharge depends absolutely on these factors.
The rapidity of each successive discharge depends on the arrange-
ment of the oscillator system or circuit in which the current flows.
In a Leyden jar only one series of oscillations can be had upon
discharge, unless there is provided some method for recharging the
jar, as a frictional machine or an induction coil. In non-syntonic
systems of wireless telegraphy the period of oscillation need not be
given special attention,
since the length of wave
emitted may be any one
of a number of lengths,
but the important feat-
ure is the arrangement
of the emitter or oscil-
lating system. A sys-
FlQ. 49.-STRONGLY DAMPED OSCILLATIONS.
cillator and a poor radiator or a poor oscillator and a good radiator.
As an illustration, the long vertical aerial wire which forms one
arm of the oscillator system may produce only two or three
oscillations before the damping coefficient causes the surging cur-
rent to fall to 0 as
shown in Fig. 49, ow-
ing to its large capac-
ity.1 On the other
hand, a closed circuit,
such as is employed in
Lodge's syntonic jars,2
is a very persistent os-
cillator, and is Shown FlG' 5°— FEEBLY DAMPED OSCILLATIONS.
graphically in Fig. 50; but as a radiator it is very feeble, for
its energy is not quickly dissipated by conversion into electric
Marconi Society of Arts, London, May 15, 1900.
"Lodge, The Work of Hertz.
52
WIRELESS TELEGRAPHY.
FIG. 51. — AMPLIFIED ELEC. OSCILLATIONS.
waves as in the case of an open circuit oscillator, and so thirty or
forty oscillations may take place in the system before the energy
is damped out. The value of the damping coefficient has been de-
termined mathematically by Herr
V. Bjerknes1 from the calcula-
tions of an electrometer inserted
in the micrometer air-gap of "a
Reiss detector.2 If the oscillator
of a closed system is in syntony
or tune with a Eeiss micrometer
detector the persistency of oscilla-
tion in the detector will be very
great as the curve, Fig. 51,
shows.
TRANSFORMATION. — Another property invested in electric oscil-
lations is that of transformation or conversion ; just as low potential
commercial alternating currents may be stepped-up or stepped-
down, so, also, may oscillating currents be transformed into a
higher or lower potential; the principles of alternating current
transformation are well known and consist in passing a current
through a primary coil which causes the space between the turns of
wire to become alternately charged and discharged with magnetic
flux, the coil and core thus being magnetized in opposite directions ;
this reversal of magnetism of the core induces an e. m. f. in the
secondary coil, increasing or decreasing the potential according to
the relative number of turns of wire wound on the primary and
secondary coils, the frequency remaining the same. This is like-
wise true of electric oscillations.
To increase the frequency of the oscillations the disruptive dis-
charge must be resorted to. Before the spark passes in an oscillator
system the frequency of the current is the same as the frequency of
the vibrations of the interruption where a direct current is employed,
or the alternations of current in the secondary equals that in the
primary circuit where a primary alternating current is used. This
frequency is enormously increased when the spark takes place, con-
verting the period of reversals from a few hundreds per second to
hundreds of thousands per second. A higher potential may be
iBierknes, Wiedemann's Annalan, 44: 1891.
*See Chapter II of Hertz' Electric Waves.
ELECTRICAL OSCILLATIONS.
53
produced by connecting the secondary terminals of the coil 7 in
parallel with a number of condensers, L L L L, or Leyden jars hav-
ing the sparks in shunt, as shown in Fig. 52, so that the inside
coatings of both series of jars are connected by both terminals of
the secondary coil and the outside coatings are connected with a
few turns of coarse wire forming the primary P; if now a second
frame is wound with a larger number of turns of fine wire, and
this secondary transformer is placed parallel to that of the first
coil the potential of the oscillatory current will be very greatly
increased; if a Leyden jar M is introduced in the secondary cir-
cuit and a spark-gap arranged at F, a second disruptive discharge
will occur and the frequency obtained by the spark S will also be
increased many fold, and a high-potential, high-frequency current
results. The Tesla-Thompson effects are produced in this way, and
Fio. 52. — TRANSFORMER FOR OSCILLATIONS.
it is evident that any potential and any frequency may be easily
produced.
KATE OF RADIATION OF ENERGY. — The rate at which an open
circuit oscillator emits its energy in the form of electric waves is
enormous, as the following deduction of Hertz will show. By
employing a dumbbell oscillator 30 cm. in diameter connected with
a spark-gap of 1 cm. by means of two rods each 50 cm. in length
he was enabled to charge the system to a potential difference of
36,000 volts. Just before it breaks down the air-gap of the charged
oscillator represents an amount of energy equal to f^ of a joule.
At the moment the spark passes the electric charge is set in
motion in the oscillator and it radiates energy in each half of an
54 WIRELESS TELEGRAPHY.
oscillation equal to 2,400 ergs or -^~ joules as indicated by the
formula
ax3
where Q is the charge of each sphere, I the length of the connecting
rods, and X the length of the wave emitted, which for the size of
the oscillator employed was ascertained to be 480 cm.
If each half oscillation radiates energy equal to ^ joules, then
in 11 half oscillations or 5% complete cycles half of the electrical
charge of the oscillator will have been emitted, and it is evident
that before the 10 complete cycles are completed practically all the
energy will have been transformed into electric waves. Fleming
shows that since the length of the wave is 480 cm. and the
velocity of propagation is 3 X 1010 cm. per second, the period
of time occupied by ten oscillations is sixteen hundred millionths
of a second, and in this exceedingly short space of time the oscillator
has emitted energy equal to about ~~ of a joule, or at a rate of
almost 45 horse-power. As an illustration of the rate at which the-
oscillator would have to be supplied with energy to keep up with
its enormous output so that the emission of the waves would be
continuous, it may be stated that 25,000 foot-pounds per second
would be required, an amount equal almost to that required to light
500 16-candle-power 100-volt incandescent lamps simultaneously.
But, as a matter of fact, the oscillator system of an ordinary
wireless telegraph system sends out trains of electric waves with
long intervals between them, while the secondary is charging the
oscillator preparatory to sending out another train of waves.
DECREMENT OF ELECTRIC OSCILLATIONS. — The decrement of
electric oscillators, or the rate of damping in open circuit oscillators,
showing the ratio of amplitude for each successive oscillation, has
been determined by Plank and .others. From the formula
_16ir*/2C
3X"
in which C is the capacity of the oscillator, / the length of the con-
necting rods, and X the length of the wave, it will be seen that large
capacities, large inductances, or both, are essential for prolonging
the oscillations.
ELECTRICAL OSCILLATIONS. 55
SKIN EFFECT IN OSCILLATORS. — An interesting experiment by
Hopkins and Wilson in 1895 showed that in a conductor of iron
or other metal a magnetic field produced by a magnetizing force re-
quired a large time value for the flux to reach the centre. If the
conductor exceeded a certain diameter and was placed in a magnetic
field, which constantly and rapidly changed polarity, the magnetism
would not extend to the centre.
An analogous effect is produced1 when a high-frequency current
surges to and fro in an oscillator system ; when such a condition pre-
vails the current penetrates the metal only a fraction of a mm.,
and this is termed the skin effect. In an experimental investigation
of the skin effect in oscillators Chant2 tested both cylindrical and
spherical oscillators. In these forms he compared their metallic
shells with those made of solid metal, and found oscillator doub-
lets made of gold leaf equally as efficient as those in the solid form.
In 1886 Lord Rayleigh3 gave a mathematical formula for com-
puting the effective resistance and the effective inductance per unit
of length of a circular section of wire when traversed by an alter-
nating current of known frequency.
Fleming, Journal of the Society of Arts. 1900.
2Chnnt, American Journal of Science. 1901.
3Self-Induction and Resistance of Straight Conductors. Phil. Mao.,
1886.
CHAPTER VI.
OSCILLATORS.
PHYSICAL.
DEFINITION OF OSCILLATOR. — The term oscillator, in wireless
telegraphy, is applied to any electrically charged body where the
charge moves to and fro at a high rate of alternation in restoring
the potential level or electric equilibrium. Here the body has a
maximum and a minimum charge at two different points at the
same instant.
OSCILLATORS. — There are an almost infinite number of sizes and
forms of oscillators, ranging from the sun, which is the largest,
down to the smallest particle of matter, be it atom or corpuscle.
The sun, considered as an oscillator, emits electro-magnetic waves
of such great length that they have never been observed experimen-
tally, although the wave length has been determined by calcula-
tions from the size and conditions of it as an electrically charged
sphere, producing oscillations of a definite frequency, and, therefore,
waves of given length." The atom charged with electricity, when
disturbed by heat, impact, or other means, agitates its potential
level, and, being so very minute, the oscillation is quickened until,
ior the sake of clearness, it is now termed vibration and produces
electro-magnetic waves that are visible, or light waves.
Between the sun as a mass and an atom of matter, all other
charged bodies, when the charge is disturbed, produce oscillations
differing in degree in the period of each reversal of the charge.
To produce definite oscillations for wireless telegraphy, an ap-
paratus must be employed for charging a body to its maximum
potential and then setting the charge into motion; this is accom-
plished by means of an oscillator.
OSCILLATOR SYSTEMS. — In the discharge of a Leyden jar it was
shown that the difference of potential was equalized through the
spark-gap, the wire or tongs forming the conductor connecting the
inside and the outside of the jar. This constitutes the oscillator
56
OSCILLATORS.
57
system of a Leyden jar. In the discharge of an induction coil the
oscillator system is a modification of the jar just cited, but ar-
ranged to suit the exigencies of the case. The oscillator system
employed by Hertz consisted, as has been shown, merely of two brass
HP °'n
Fio. 53. — OSCILLATOR SYSTEM.
spheres, A, A', Fig. 53, two larger metal spheres, B, B', connected
with the brass wires and rods, C, C' ; D, D' are the binding posts
of the secondary terminals of the induction coil, and do not form
a part of the oscillator system proper, but are merely the connection
between it and the secondary coil, for the purpose of charging the
system with electricity to a high potential. Thus the dividing line
between the secondary of the induction coil or transformer and the
oscillator system is the binding posts. To obtain the best results
with the minimum amount of energy, much effort has been spent
not only on the oscillator system as a whole, but on individual parts
of it ; the following represent the different forms as used by Hertz
and by his successors to the present time.
HERTZ'S OSCILLATOR. — Another form of oscillator, shown in
Fig. 54, was devised by Hertz for his first experiments. The spheres
B and B' may be replaced by any shape or size having capacity,
though Hertz favored the adjustable oscillator shown in Fig. 54,
FIG. 54. — HERTZ'S ADJUSTABLE OSCILLATOR.
where B and B' are arranged to slide on the rods C and C' permit-
ting the value of inductance and capacity to be varied at will and the
system thus tuned or syntonized with the resonator or spark-gap
detector. In the Hertz oscillator the spheres were of sheet zinc
30 cm. in diameter, the spark-gap balls 3 cm. in diameter connected
58
WIRELESS TELEGRAPHY.
with rods 50 cm. long. This form is called the Hertz dumb-bell
oscillator.
RIGHT'S OSCILLATOR. — Auguste Righi in his photo-electric re-
searches devised the oscillator shown in Fig. 55. It consisted of
FIG. 55. — RIGHT'S OSCILLATOR.
two large spheres, A, A' ', with a spark-gap between them 1 mm.
in length and two secondary terminal spheres, B, B' ', a cm. from
A and A' respectively. In this oscillator two sets of electric waves
are emitted, those emanating from the large spheres A, A' and
those emitted from the smaller spheres B, B' , including the rods
leading to the secondary terminals C, C'. Both of these sets of
oscillators are, of course, in alignment with the oscillator system,
that is, the surging takes place along the line of propagation.
LODGE'S OSCILLATOR. — Another form of oscillator devised by
Lodge is shown in Fig. 56, nnd is similar to Righi's, but has
FIG. 56.— LODGB'B OSCILLATOR.
only one central sphere, instead of two, which is much larger
and is supported between two smaller spark balls in close proximity
on either side. When the disruptive discharge current oscil-
lates through the system represented diagrammatically by the
letters A B C D E F, waves are emitted by the system from A to F,
but a secondary definite charge surges from side to side on the ball
C D, sending out another train of waves with considerable vigor,
but the oscillations die out quickly, since it is readily seen that
such a charged body is a good radiator for the electric waves. Two
or three oscillations only will take place in the ball when the charge
OSCILLATORS.
59
will have been dissipated in the form of electric waves, reaching
the vanishing point or zero in finite time theoretically, but prac-
tically in a very small fraction of a second. From tests of
capacity and inductance it has been deduced that the wave length
produced by these charged metal spheres is about one and one-half
times the diameter of the sphere.
MULTIPLEX OSCILLATOR. — M. Albert Turpain1 describes an
oscillator for emitting an octave of electric waves or waves of differ-
ent lengths simultaneously. Fig. 57 shows the arrangement
for producing multiplex waves, or, as Turpain terms it, a
multiplex oscillator. Before the laws of the coefficients were
Fia. 57. — MULTIPLEX OSCILLATOR.
interpreted by J. J. Thomson, Lamb and Lodge, the sup-
position relating to wave lengths radiated by an oscillator
was that they were of many and varying lengths, like the
composite wave lengths of light, producing white light, but it was
finally determined that waves of a given length only were emitted by
an oscillator of specific proportions. The monochromatic oscillator
may therefore be compared to an octave of musical notes, each
producing a distinct wave length. In the monochromatic or multi-
plex oscillator there are a number of spherical metal shells of differ-
ent diameters, each of which is supported on an ebonite or other
dielectric and the whole immersed in an oil chamber. When the
disruptive discharge takes place through the system, the oscillatory
charge of each of the spheres radiates a train of electric waves of a
definite length. These waves may be detected and picked out, or
selected by means of a Hertz resonator at short distances ; and this
offers a good illustration of selective or syntonic signaling.
CONTINUOUS DUMB-BELL OSCILLATOR. — Another form of
dumb-bell oscillator without the usual air-gap is shown in Fig. 58 ;
it may be charged and the charge caused to oscillate as in the
lLes applications Pratiques des ondes electriques, Turpain.
60
WIRELESS TELEGRAPHY.
spherical oscillator of Lodge, i.e., by having the terminals of the
FIG. 58. — DUMB-BELL OSCILLATOR.
secondary coil end in small brass balls, oppositely disposed, and
with the oscillator between them.
BOSE'S OSCILLATOR. — Prof. J. Chandler
Bose designed an oscillator for producing ex-
ceedingly short wave lengths. It is illustrated
in Fig 59, and consists of a small ball of
platinum 2 mm. in diameter supported between
two smaller balls of the same metal; it is
really a miniature form of Lodge's oscillator,
previously described. With this oscillator Bose
has polarized the electric waves by means of
asbestos, epidote and other fibrous minerals.
EXPERIMENTAL OSCILLATOR. — An oscillator for experimental
work, emitting 300 million waves per second, each having a length
of one meter, is shown in Fig. 60. It consists of two identical arms,
A, B, each of which has a sphere 8 cm. in diameter at the end and
FIG. 59.—
BOSK'S OSCILLATOR
FIG. 60. — EXPERIMENTAL OSCILLATOR.
connected with spark-gap balls by a brass bar 1 cm. in diameter and
6 cm. in length ; the spark-gap balls measure 2 cm. in diameter each,
and, used with a 15-cm. spark-coil should be set 8 mm. apart.
With a larger coil they should be set farther apart, and used with a
smaller coil the gap should be correspondingly decreased.
Instead of employing the large spheres for the oscillators, it is
often more convenient to use circular disks of sheet metal, or square
or oblong plates may be used. The formula? for obtaining the
specific inductive capacity and its permeability or inductance of
these values will be found in the following chapter. Leaving the
experimental forms of oscillators, we now come to those designed
for practical work in wireless telegraphy, or that class found neces-
OSCILLATORS.
61
sary for radiating waves to great distances, or at least to such dis-
tances as are required for commercial purposes.
MARCONI'S OSCILLATOR.— To Marconi belongs the credit for
having been the first to discover the
requirements necessary to fulfill
these exacting conditions. The sim-
plest form of practical oscillator for
wireless telegraphy is shown in Fig.
61. It consists merely of a vertical
wire, fifty or one hundred feet in
length, and extending into the air,
the lower terminal of which is con-
nected with the spark-ball 2; a
second spark-ball, 3, separated a few
mm. from the first, forms the spark-
gap 4, and from this a wire leads to
the earth at 5.
OPEN AND CLOSED OSCILLATOR
SYSTEMS. — All the oscillator sys-
tems described above are known as
open-circuit oscillator systems, that
is to say, they have a free period
of oscillation, and therefore radiate
waves with great energy, though the
oscillations are quickly damped out.
There is another class of oscillators
termed closed-circuit oscillator sys-
tems, in which the period of oscilla-
tion is limited to the size of the circuit ; if this has a natural period
equal to that of the impressed oscillations these will be prolonged
for a considerable length of time before the energy is dissipated;
closed-circuit oscillators are, therefore, very feeble emitters of elec-
tric waves.
Lodge in his researches on the lightning rod1 devised many ex-
periments; one especially is of interest here, bearing as it does on
the action of closed circuits forming oscillator systems. In Fig. 62
is shown the oscillator system of Lodge's syntonic jars; 1 is an
ordinary Leyden jar, the inner coating of which is connected to
one ball, forming the spark-gap 2 ; a circuit, rectangular or of other
JThe Lightning Rod. O. J. Lodge.
Fio. 61. — MARCONI RADIATOR.
WIRELESS TELEGRAPHY.
suitable shape and dimensions, leads from the upper ball and
terminates in a connection with the outside coating of the jar.
If the jar is now charged and then allowed to discharge through
FIQ. 62. — CLOSED CIRCUIT OSCILLATOR.
the spark-gap 2 and the circuit of wire, the oscillations will be very
persistent in the circuit, surging to and fro many times before
reaching 0, and emitting waves that have but little penetrative
power, for, as previously pointed out,
such a closed circuit spends its energy in
oscillation instead of in radiation.
Slaby, during his early experiments,
employed an oscillator system in his trans-
mitting apparatus for practical wireless
telegraphy which was similar to the Lodge
syntonic emitter jar, except that its pro-
portions were much larger and its energy
supplied by a very large induction coil.
An inductance coil, E, Fig. 63, was added
at the top for the purpose of conducting
away and dissipating all electric waves of
a length greater than those required to
fulfill the law of harmonics represented
by the terminal of the vertical wire A, and
the earthed end, B. It will be seen that
a practically closed circuit was formed be-
tween A B C D, the earth closing the cir-
cuit between B and D. Slaby has now
abandoned this form for an open oscillator system, based on the
original single vertical wire.
Nevertheless, in wireless telegraphy where syntonization or a
tuned system is desired, it is quite advantageous to operate with
closed-circuit oscillators, and Marconi in his recent attempts to
produce a commercial syntonic system has evolved from the simple
TO (.o\tt :
SLABY'S
FIG. 63.—
CLOSED
EMITTER.
CIRCUIT
OSCILLATORS. 63
Leyden-jar circuit of Lodge an apparatus so constructed as to
effect a compromise between 'the open-circuit and the closed-circuit
oscillator, producing in turn an emitter having an intermediate
amplitude between the severely damped oscillation of the open-
circuit system and the prolonged period of oscillation of the closed-
circuit system, thus yielding trains of waves of considerable pene-
trative power. In nearly all commercial systems now in actual use,
one terminal or arm of the oscillator is earthed. Lodge deemed
the earth connection unnecessary, and deduced the conclusion that
if the spark-gap was elevated midway between the oscillator arms,
and these were mutually balanced in capacity and inductance, the
resultant effect would be equal in efficiency to that of a grounded
open-circuit system. This oscillator will be described under the
head of Syntonization, Chapter 19.
FIG. 65. — DISSYMMETRICAL SYSTEM.
SYMMETRICAL AND DISSYMMETRICAL OSCILLATOR SYSTEMS. —
Oscillators, where the arms are balanced equally in resistance, in-
ductance and capacity, as in the open-circuit type of Hertz, are
termed symmetrical systems. Where the coefficients vary in value
in the opposite arms of the same system, they are termed dis-
symmetrical systems. All commercial systems are dissymmetrical,
since the arm connected with the earth is loaded with an additional
capacity by the condenser action of the earth itself. This may be
attributed to two factors; (1) the capacity of the earth slows down
the oscillations, and (2) Hertz has shown that by physically alter-
ing the coefficients of capacity and inductance,1 in accordance with
Lord Kelvin's deductions2, a harmonic relation or syntonization
could be effected between the emitter and detector systems, due to
resonance, and thereby increasing the efficiency very materially. The
diagram Fig. 65 illustrates a dissymmetrical oscillator, having a
Leyden jar or glass-plate condenser, A, inserted in one arm and
an inductance coil, B, in the opposite arm. Variations of capacity
and inductance may be made to fulfill any condition which may
arise in practice required by the law of resonance.
1 Hertz's Electric Waves.
'Kelvin, Transient Electric Currents, 1853.
CHAPTER VII.
CAPACITY, INDUCTANCE, AND RESISTANCE.
HISTORICAL.
HISTORY OF CAPACITY. — In 1776 Coulomb, whose name has
Bince been given to the unit of electrical quantity, proved by a
series of brilliant tests, based on the two-fluid hypothesis of elec-
tricity, that the action of an electric charge varies in the inverse
ratio as the square of the distance. He likewise investigated theo-
retically and experimentally the distribution of electricity on the
surface of spheres. In 1782 Laplace and Biot enlarged upon these
researches, deducing important mathematical conclusions. Poisson
next brought the subject under analysis based on the two-fluid
hypothesis to a higher degree of perfection. In 1828 Green1 ex-
tended the analysis of Poisson and Laplace and mathematically
evolved the electrostatic theory based on the law of Coulomb.
Faraday in 1837, with his intuitive insight, concluded that the di-
electric through which induction takes place was polarized and that
the strain or stress was transmitted between the positive and
negative charged bodies by the polarized atoms of the dielectric.
This strain is often seen in the piercing of the glass dielectric of the
Leyden jar, as well as in the residual charge of the glass.
Green's theorems and Faraday's deductions were enlarged
and improved upon in 1845 by Lord Kelvin, who, with great
mathematical power, showed how the electrostatic strain of a
dielectric was in absolute accord with the theory annunciated by
Green. Following Kelvin are the researches of Maxwell. In 1873,
in his Electricity and Magnetism, he fully elucidated his beautiful
theory of the action of a dielectric medium which is contained in
the proposition that in transparent media whose magnetic induc-
tive capacity is very nearly that of unity the dielectric capacity is
equal to the square of the index of refraction for light of infinite
1Green's Application of Mathematical Analysis to Electricity and Mag-
netism.
64
CAPACITY, INDUCTANCE, AND RESISTANCE. 65
wave length. Hertz determined experimentally that by varying
the capacity the electric oscillation could be modified and therefore
the length of the wave emitted.
HISTORY OF INDUCTANCE. — The history of self-induction, or, as it
is now termed, inductance, extends only to Henry's time. Joseph
Henry observed the phenomenon and published an account of it as
early as 1832. * The remarkable fact that a long conductor had an
intensifying influence on the current, and especially if the wire
was wound in the form of a spiral and interposed in the circuit,
Henry attributed to the long wire becoming charged with electricity
which by its reaction on itself projects a spark when the connection
is broken1. The same discovery was made a year or two later by
Fleeming Jenkins, who communicated to Faraday the fact that he
was able to obtain shocks when he included the coil of an electro-
magnet in the circuit, though no appreciable effect was obtained
when the coil was removed. In 1834 Faraday published in the
Philosophical Magazine the result of his researches on self-induction,
and asserted that the same law was in evidence when a simple coil of
wire without a magnetic core was substituted for the electro-mag-
net, and that a similar effect, though less pronounced, was obtained
when a very long straight wire was employed. Faraday believed
that self-induction was due to magnetism, and that the current in
rising in the circuit produced a number of lines of magnetic force
which opposed that of the battery and caused the current to rise
slowly. He believed also that, when the current begins to decrease,
the number of lines of force begins to decrease and the e. m. f . of in-
duction is called forth, which tends to prolong the current, weak-
ening the e. m. f. at starting and exalting it at stopping. Edlund
investigated the integral e. m. f. of inductance on making and
breaking the circuit and found that they were equal. Max-
well treated the subject exhaustively from a mathematical stand-
point, and introduced a convenient method for showing the effects
and measuring the inductance by using a Wheatstone bridge.
Helmholtz was the first to treat the subject experimentally and
mathematically. Lord Kelvin published his deductions in the
Philosophical Magazine in a paper entitled "On Transient Electric
Currents/' in which he discussed the discharge of the Leyden jar
and elucidated other important phenomena. For instance, he
recognized the influence which the electro-dynamic capacity, or,
1PhilosopMcal Magazine, November, 1832.
66 WIRELESS TELEGRAPHY.
as we now term it, inductance, of the oscillator had upon the
discharge, and he established an equation of energy which expresses
the fact that the energy of the charged body at any instant is partly
dissipated as heat in the discharging circuit and partly conserved
as current energy in that circuit. Hertz, in his paper, "Very
Rapid Electric Oscillations,"1 considers the theory of Kelvin,
Helmholtz and Kirchhoff, in which the inductance is considered in
electro-magnetic' r^asure, and capacity, in electrostatic measure and
applied them to actual cases of experimental research.
HISTORY OF RESISTANCE. — Before the year 1827 the nature of
the electric current was expressed in terms of intensity and quantity.
In 1827 Ohm enunciated his great law relating to the resistance
of a circuit to a steady direct current, which, fully stated, is I = -
R
The verification of Ohm's theory of the electric current and im-
provements in instruments for measuring resistance are largely
due to Wheatstone, Kelvin, Matthieson, and others. In 1841 Joule
established the law relating to the heat evolved per second with
the current strength and the resistance of the wire, which may be
stated by the formula H=RPt. The experiments of Joule were
carefully repeated to insure accuracy by Becquerel, Lenze and Botts.
THEORETICAL.
DEFINITION OF CAPACITY. — In the succeeding explanations,
formulae and examples, the term capacity will be understood to
mean electrostatic capacity, unless otherwise designated. The
electrostatic capacity of an oscillator system is the quantity of
electricity which will raise its potential to a definite amount. A
gas-tank may be taken as an analogue for an electric oscillator. The
electricity will produce in an oscillator system a difference of po-
tential depending on its size, form, and the electrical pressure ex-
erted upon it at the terminals of the secondary coil charging it.
The capacity represented by K, of a conductor, condenser, or
oscillator is directly proportional to the quantity of electricity Q,
which it will hold at a given potential V; or, K = ^ ; or the
quantity of electricity to charge an oscillator to a given potential is
'Hertz' Electric Waves.
'Kirchhoff in 1849 was the first actually to measure the resistance of
a circuit, which he did by a comparison of a resistance with a coefficient
of mutual induction, the time measurement being that of the period of
oscillation of a galvanometer. — Enoy. Brit.
THE
UNIVERSITY
OF
, INDUCTANCE, AND RESISTANCE. 67
equal to the capacity of the oscillator multiplied by the potential
through which it is raised, or Q = KV.
The charging of the oscillator is the first effect of the high-
potential current producing a distribution over the surface like the
charge of a condenser. The capacity depends on the length and
surface of the oscillator, its proximity to other conducting bodies,
and its relative distance from the earth. The capacity retards the
frequency of oscillation because the charge must be neutralized at
each disruptive discharge before the oscillatory current can exert
a reflex action in the opposite direction.
UNIT OF ELECTROSTATIC CAPACITY. — The coulomb is the unit
of electrical quantity and is equal to (1) the charge contained in
one farad capacity when subjected to a pressure of one volt, or (2)
the quantity passing in one second through a resistance of one ohm
under an e. m. f. of one volt, or (3), the quantity of electricity con-
veyed by one ampere of current in one second. The farad is the
unit of capacity and represents a surface of such dimensions that
one coulomb will produce a potential of one volt. The microfarad,
or one one-millionth of a 'farad, is used in ordinary measurements,
since the farad is too large for practical purposes.
DEFINITION OF INDUCTANCE. — Self-induction, or inductance,
is that property of an electric current which finds its material
counterpart in inertia. A current in a conductor or an elec-
tric charge of an oscillator requires a definite- time to start1;
again, when a current is flowing in a wire or a charge oscil-
lating in a system, time is again required for the flow to cease
or the charge to fall to zero. In virtue of this quality of inductance,
the oscillation of an electric charge causes a magnetic field to be
formed by the absorption of electric energy. The inductance of an
oscillator depends on (1) the form or shape of the system; (2)
the magnetic permeability of the space surrounding the oscillator
system — this is usually the air, representing unity; and (3) the
magnetic permeability of the oscillator itself. In high-potential,
high-frequency currents like those due to a disruptive discharge,
inductance becomes a most potent factor and causes the current to
act, with relation to time, like a heavy body under the starting
action of any force. The electro-magnetic energy present in any
circuit is equal to one-half of the square of the current multi-
Modern Views of Electricity.
68 WIRELESS TELEGRAPHY.
plied by the inductance. The oscillating current, then, is the factor
representing force, hence inductance must be represented by the
dimension of length ; the practical unit of inductance corresponds,
therefore, to a length equal to the earth's quadrant, or 109 cm., and
was formerly called a quadrant or secohm, but is now known as a
henry; the absolute unit of inductance corresponds to one cm.
Usually oscillators are formed of some metal or metals that
have no magnetic properties; they are likewise usually exposed in
free air, which has a constant magnetic permeability ; where the in-
ductance is constant, its value depends only on the size and shape of
the oscillator system. In this limiting case the total inductance of
the oscillator is proportional to the magnetizing force and the
magnetic resistance. In the construction of oscillators for high
frequencies, flat strips of copper may be used to advantage, as
it has been shown that a form of this type is a good emitter, since it
offers a greater surface for absorption to the air than a round con-
ductor having an equal cross-section. When the geometric form
of an oscillator remains unchanged, as it does in all practical cases,
and the lines of magnetic force pass through homogeneous di-
electrics, as the air, and uniform diamagnetic metals, of which the
oscillators should be made, the inductance is constant. The mag-
netic permeability of a body depends on its conductibility to the
lines of magnetic forces. The ratio between the intensity of mag-
netic induction and the force producing the magnetization may be
stated thus : p = ^, where p is the permeability, B the produced
magnetization, and H the magnetizing force. The permeability
of oscillators, assuming them to be made of non-magnetic metals,
is practically that of air, and as the magnetization increases the
magnetic permeability decreases.
DEFINITION OF EESISTANCE. — The law of resistance stated by
. Ohm for direct steady currents is that the resistance equals the
e. m. f . divided by the current, or R = j, or, 7 = |-. The unit
of resistance is the ohm, and a resistance of one ohm would limit
the current flow to one coulomb per second when the e. m. f. is
equal to one volt. Another law must be recognized in the action
for alternating currents of high frequency, as these do not follow
absolutely the laws of resistance for low-voltage direct currents;
the second law is known as Joule's law, and asserts that the
heating power of a current is proportional to the product of
CAPACITY, INDUCTANCE, AND RESISTANCE. 09
the resistance and the square of the current strength. In lim-
ited cases Ohm's and Joule's laws agree; but as Lodge has
pointed out,1 in cases of varying magnetic induction, some of the
energy is stored, all is not dissipated, and the two definitions do
not agree. An oscillator in action dissipates a very small part of
the current as heat, and a much larger portion in the form of
waves radiated into space. Both the heat dissipation and the
electric radiation are included in the law of resistance.
THE EFFECT OF CAPACITY, INDUCTANCE, AND RESISTANCE ON
ELECTRIC OSCILLATIONS. — Lord Kelvin has given in his paper,
"Transient Electric Currents/'2 an equation showing that the rate
of release of energy of a charged jar is at any instant equal to
the dissipation of energy in the discharge circuit, or, as it is now
termed, the oscillator system, added to the rate of change of the
kinetic energy in the circuit. Kelvin's deductions were based on
the experimental evidence of the action of a Leyden jar, but the
equations hold good for the oscillator systems of induction coils as
well. Let the capacity of a jar or oscillator be expressed by C, its
resistance bv "R, its inductance by L, the quantity of electricity
in the condenser at any time t by q, and the current in the oscillator
circuit by I, then by the following differential equation we have the
above stated thus:3
I .
where T is written for £, TT, for CE, and <2 and £ for the first
and second time derivatives of q. The solution of the above
equation enables the value of the quantity of electricity or the
charge of the jar or in the system to be found at any instant. It is
evident that the constants may be so proportioned that the discharge
may describe a smooth curve in reaching zero, or the discharge may
describe a curve which is periodic and alternate until it reaches
dodge's Modern Views of Electricity.
^Philosophical Magazine, 1853.
'Fleming, Journal of the Society of Arts, 1900.
70
WIRELESS TELEGRAPHY.
zero. The two solutions of the equation are shown graphically in
rectangular coordinates in Figs. 66 and 67. Fig. 66 represents the
"/V-,
/ \TIME:. 7^\T
\ / ^
U-'
FIG. 66. — DISCHARGE THROUGH A
LAROB RESISTANCE.
FIG. 67. — DISCHARGE THROUGH A SMALI.
RESISTANCE.
discharge through a large resistance and Fig. 67 the discharge
through a small resistance.
FORMULA FOR CALCULATING THE CONSTANTS. — For the practi-
cal determination of the constants governing the period of oscilla-
tion, recourse may be had to the following formulae. Let
K = capacity.
R = resistance.
L = inductance.
n = number of oscillations per second.
Then oscillations will occur if
R<!* ML
\ IT
and will not occur if
In this latter case a unidirectional current will reach zero
gradually.
The frequency of oscillation of the charge of the oscillator may
be obtained from the formula :
In practice the resistance is usually very small and may be
considered negligible ; and, therefore, making R = 0 in the above,
we have
CAPACITY, INDUCTANCE, AND RESISTANCE. 71
FORMULA FOR CALCULATING CONSTANTS OF OSCILLATORS. —
Since K, L and R depend on the size and shape of the oscillator, it is
often necessary to construct an oscillator for producing oscillations
of a definite frequency. In this case let
1 = length of rod (a a Fig. 68).
d = diameter of rod,
r = radius of spheres (b b' and c, c'.)
s = distance from center to center.
then
L=21 (lo? '-l).
and K = %rl
Where the capacity areas are of other forms than the sphere
the value of K is for a
thin circular disk, 2 radius.
IT
thin square " 0.36 side of a square.
thin oblong " slightly greater than square of same area.
MEASUREMENTS. — It is quite difficult to measure the inductance
and capacity of oscillator systems by comparison with standardized
FIQ. 68. — CONSTANTS OF OSCILLATOR.
units of these quantities since K and L are usually of a very small
value. The resistance of the system may be easily measured, how-
ever small its value, but where R is small it may be neglected in
calculations for ascertaining the frequency of oscillation. In all
measurements, as in deductions, the oscillator system is understood
to include the connecting wires leading to the binding posts. In
measuring oscillators such as spheres or isolated systems the
terminals of the testing instruments should be placed in contact
with the opposite peripheral surfaces. In discontinuous oscillators,
i.e., where a spark-gap intervenes, as in the Hertzian type, the con-
stants of each arm may be measured from the terminals leading
to the binding posts of the secondary coil, and each arm may be
measured separately or the gap bridged by causing the spark-gap
balls to form a contact.
72 WIRELESS TELEGRAPHY.
CAPACITY. — There are several excellent methods for measuring
electrostatic capacity; among those usually employed are the direct
deflection method, the divided discharge method, and the Grott,
Siemens and Thomson methods ; the least difficult way, though not
the most accurate, is by the direct-deflection method, where the
discharge from an unknown capacity is compared with the discharge
from a condenser of known capacity.
MEASUREMENT OF CAPACITY — If the inductance is small com-
pared with the capacity, as in the case of a plate condenser, the
bridge method may be used. If the inductance cannot be neglected
in comparison with the capacity, as in the case of some Leyden jars,
the ballistic galvanometer method must be used.
In the bridge method, the arrangement must be as shown in
IPig. 69, where C^ is the condenser of unknown capacity; C2, a
6. S/ K.
FIG. 69. — BRIDGE FOR CAPACITY MEASUREMENTS.
standard condenser ; Rs, a constant non-inductive resistance of suit-
able magnitude ; R4, a variable non-inductive resistance ; A, a source
of periodic current ; T, a telephone receiver, and Kf a key to open
and close the circuit Rs and R4 can conveniently be the fixed and
variable resistances of a Wheatstone bridge of the box form. The
•commercial alternating 110-volt current can be used to supply
periodic current if proper precautions are taken to prevent too
large a current passing through the bridge. This current should
not exceed a tenth of an ampere, otherwise there will be danger of
burning out the resistance coils of the box. The desired result may
fee obtained satisfactorily and safely by the method of the po-
tentiometer. This arrangement is shown in Fig. 70, where m^ and
m2 are the alternating current mains and r a resistance of 100
•ohms or more. The sixth arm of the bridge is, in this case, attached
CAPACITY, INDUCTANCE, AND RESISTANCE. 73
to the two points a and b of the resistance. In this way any de-
sired difference of potential can be obtained.
If a small induction coil is used to generate the periodic current,
the secondary of the coil is inserted in place of A in Fig. 69.
FlO. 70. — POTBNTIOMETliR METHOD.
In either case to determine the unknown capacity, the resistance,
EI must be varied until no sound is heard in the telephone, when
the circuit is closed by the key, Tc. Sometimes it is impossible to
get rid of the sound entirely. In this case that value of #4 must
be taken which makes the sound a minimum.
When this value of R4 has been found we have the well-known
relation,
that is
R4XC,
R,
That is, the unknown capacity is equal to the standard capacity
FIG. 71. — DIRECT CURRENT METHOD.
multiplied by the variable resistance and divided by the constant
resistance.
If it is inconvenient to use a periodic current and telephone,
a battery, B, and galvanometer, G, may be used as shown in Fig. 71.
74 WIRELESS TELEGRAPHY.
A value of R4, is then found such that on opening and closing the
key, Ic, there is no deflection of the galvanometer.
In the ballistic galvanometer method, the condenser to be
measured, C19 is put in series with a battery, E, a galvanometer, G,
and a key, fcx; see Fig. 72. A second key, Ic2, is put around the
Ka.
Fio. 72. — BALLISTIC GALVANOMETER METHOD.
condenser C19 so that it may be discharged when desired.
In making the measurement, the deflection d± is noted when
the key Jc^ is opened. C^ is now replaced by the standard condenser
C and the deflection d is noted. When we have
C, d,
C2 X
CAPACITY OF AN AERIAL. — In the following diagram, Fig. 73
a, is the antenna;
c, a commutator (rotating) ;
g, a galvanometer ;
b, a battery;
E, the earth plate.
The antenna is charged n times a second by
the rotating commutator c from the battery b.
After every charging it is discharged through
the galvanometer g. The n discharges a sec-
ond through the galvanometer produce a
steady deflection on the galvanometer, the
value of which in terms of amperes can be de-
termined by calibrating the galvanometer.
E Call this current value of the deflection A;
Fio. 73.— CAPACITY OF wp 4-|lpn y.oyp
AN AERIAL. " e uien nave
CAPACITY, INDUCTANCE, AND RESISTANCE. 75
where q is the quantity of electricity sent into the aerial by one
charging for in one second the total quantity sent into the aerial,
or what is the same thing, discharged through the galvanometer, "is
n X q. But this is the mean current through the galvanometer.
But q = CV where C is the capacity of the aerial and V the po-
tential of the battery. Therefore we have
or
_I_
nV
This is in absolute units. To convert it into practical units we
must multiply by 106. Then we have
r IX 10*
nV~
where C = capacity in microfarad,
I = current in amperes,
V = potential in volts.
This is a simple and satisfactory method.
MEASUREMENT OF INDUCTANCE. — The inductance of a single
loop of wire, or of a small coil, may be determined by comparison
with a standard inductance in much the same way as a capacity,
by the bridge method. It is necessary in this case, however, to in-
sert an auxiliary non-inductive resistance, r, either into arm 1 or
arm 2 of the bridge. See Fig. 74, where
FIG. 74. — BRIDGE FOR INDUCTANCE MEASUREMENTS.
Lj is the unknown inductance to be measured;
Rt, its resistance;
L2, the known standard inductance;
R2, its resistance;
R3, a non-inductive constant resistance;
R4, a variable resistance.
76 WIRELESS TELEGRAPHY.
In order that there shall be a complete balance between the four
arms, that is, that there shall be no sound in the telephone, we
must have the resistances of the four arms proportional to each
other, and at the same time the inductances must be proportional
to the resistances, that is, we must have
R, R.
and
This result is obtained by alternately varying r and £4 until
there is no sound in the telephone. When this is the case, we have
If it is not convenient to use a telephone and periodic current,
a galvanometer and battery may be used as in the case of the con-
denser.
INDUCTANCE OF AN AERIAL. — It is obvious that aerials cannot be
measured directly by the bridge method suggested by Maxwell, since
both ends of the conductor must be connected in the bridge. It is
possible, however, to measure the inductance of either single, multi-
ple or other form of aerial indirectly, by measuring its capacity
and its wave-length and then .calculating its inductance from the
formula
A = 2 TT v VLG
where
X— wave length of the aerial.
v = velocity of light.
L= inductance of the aerial.
G— capacity of the aerial.
solving for the inductance L we get
~ 4^ V2C
so that if the wave length * and the capacity C of the aerial can
be obtained, the inductance L may be also ascertained.
The capacity may be measured by the method described above
and the wave-length can be found by one of several methods; of
the latter a very excellent one, based on the phenomena of reso-
nance, is due to Drs. de Forest and Ives, and is described in the
Electrical World and Engineer, for June 4, 1904.1 V~i
'On a New Standard of Wave Length. By Dr. James E. Ives.
CAPACITY, INDUCTANCE, AND RESISTANCE. 77
RESISTANCE. — The most convenient arrangement for measuring
resistances is the Wheatstone bridge, the connections and circuits
of which are given in the diagram Fig. 75. The four arms con-
stituting the parallelogram A B R and X are arranged so that
when a current from the battery flows through the circuit and the
needle of the galvanometer shows no deflection the arms A R and
B X neutralize each other and equilibrium is obtained. For calcu-
lations lower than the actual lowest value of the variable resistance
R i.e., 1 ohm, the bridge arm A is given a value of 1,000 ohms and
that of B 1 ohm. If an oscillator having a very low resistance id
to be measured it is connected to the terminals of the X arm; a
5-ohm plug is removed from the variable resistance, let it be sup-
FIG. 75. — RESISTANCE MEASUREMENTS.
posed that the needle is deflected several degrees; this shows too
small a resistance in the variable resistance compared with the un-
known resistance. Next, unplug 10 ohms, making a total of 15 ohms
in the variable resistance; the needle now swings to +, showing
the resistance too high; replace the 5-ohm plug and the needle
remains on the 0 division of the galvanometer, indicating that
the arms are balanced and that the resistance of X
ohm.
CHAPTER VIII.
MUTUAL INDUCTION.
HISTORICAL.
; ,<fi.;-.. '• . i
Mutual induction, or the action of a current in one con-
ductor on another or second current by the mutual interaction
of their magnetic fields, was discovered by Faraday. The first
remarkable experiment which finally enabled Faraday to make
this sweeping observation was the discovery of Oersted in 1819 that
a current of electricity produced a magnetic field. He found that
when a wire through which a current was flowing was held parallel
to an ordinary compass needle, the needle would be deflected at
right angles to the direction of the flow of the current. In 1820
Davy and Arago discovered, independently, the method of magnet-
izing iron by passing a current through a wire coiled around it.
Ampere was the first to give these observations a theoretical value.
In a communication dated 1825, Sturgeon described his electro-
magnet1, consisting of a piece of heavy iron wire bent into a U-f orm,
having a copper wire wound around it loosely in eighteen turns, and
connected to a battery. In 1828 Henry exhibited a small electro-
magnet closely wound with silk-covered copper wire one-thirtieth,
inch in diameter. The first experiment illustrating the phenomena
of mutual induction was made by Faraday in 1831, the apparatus
consisting of a spool of wood on which were wound two coils of
wire parallel with each other. In the circuit of one coil was inter-
posed a galvanometer ; in the circuit including the opposite coil was
a battery and a key to make and break the circuit. When the key
was pressed in the first circuit the galvanometer showed the passing
of a current in the second circuit, but in the opposite direction to
that in the primary coil; and when the circuit of the latter was
broken, the needle was again deflected in the opposite direction. In
either case the induced current had only a momentary duration.
To. explain this action of one current upon another, Faraday
Memoirs of Joseph Henry.
78
MUTUAL INDUCTION. 79
evolved his curved lines of force. Lenz in 1833 deduced his law
for the determination of the direction of currents produced by
mutual induction from the theory of Ampere ; this law follows co-
incidentally the principles of Faraday. Henry in 1840 investigated
the nature of mutual induction, devising for the purpose a series of
three coils, and named the current obtained in the second coil
a "current of the second order'" that in the third coil, a "current of
the third order'' et cetera, producing successive induced currents
up to the seventh order. Becquerel described in detail Henry's re-
searches on mutual induction in his work, Electricity and Magnet-
ism.1 Ritchie also conducted some experiments in mutual induction
about the same time. From the laws of Lenz, Neumann in 1845
developed the mathematical theory of the action of one linear cur-
rent on another. In 1846 Weber verified mathematically and
experimentally the law of induction and improved upon the galva-
nometer for the purpose of testing his conclusions. The first attempt
to ascertain the absolute value of a current in the secondary circuit
was made by Kirchhoff in 1849. The first application of the in-
duction coil to practical purposes was probably made by DuBois-
Reymond, who introduced the automatic make and break about the
year 1850 ; with this coil he made his famous electro-physiological
experiments. Wagner subsequently improved upon the interrupter,
using an independent electro-magnet in the form of a horseshoe
to interrupt the primary circuit. A year later Helmholtz worked
out the theory of induced currents in a number of limiting cases,
as did Felici in 1852. In 1853 Fizeau made the modern induction
coil what if is by his application of the condenser in the primary
circuit. In 1855 Foucault designed the interrupter which bears his
name. To Ritchie is due the credit of having devised the method
of building up the secondary coil, by winding a number of layers
and then joining them together, insulating the segments from each
other. Ruhmkorff, a German mechanician, residing in Paris,
constructed induction coils having the greatest degree of efficiency
and added the commutator for reversing the current. Finally, in
1864, Maxwell, with his wonderful conception and grasp of electro-
magnetic phenomena, deduced the principles of the electric field,
including not only mutual induction, but every phase of statical
and dynamical electricity, on which, as a whole, he constructed
the electro-magnetic theory of light.
lrTraite experimental de l'Slectricit£ et magngtisme, vol. 5.
80 WIRELESS TELEGRAPHY.
INDUCTION. — When a current of electricity flows through a
closed circuit there is produced outside the conductor a field of
magnetism and if the conductor is wound in a coil the number of
lines of magnetic force is greatly increased. If the theory is.
accepted that magnetism is merely electricity in rotation, constitut-
ing a whirl in the dielectric medium, it is easy to account for the
phenomenon of induction. As analogues of electrodynamic induc-
tion those of static induction and magnetic induction may be given.
To electrify a body by static induction it is not necessary that it be
brought into actual contact with the charged body; for instance,
let A, Fig. 76, be a body charged with positive electricity and let B
be a pith ball suspended near it. The charge of A polarizes the
FIG. 76. — STATIC INDUCTION.
dielectric, in this case the air, separating the two bodies, and
the side of B nearest A will be charged negatively and the opposite
side of B positively. This effect produces electric separation by
induction. In magnetic induction all the characteristics of a rota-
tional current, or a magnetic field due to a current flowing through a
helix of wire may be exhibited ; in other words, the curved lines of
force of both are similar in every respect. If the pole of a perma-
nent steel bar magnet, A, is brought near the end of a bar of soft
iron, B, Fig. 77, the iron becomes a temporary magnet without
actual physical contact with the permanent magnet by induction,
and with its poles oppositely disposed to those of the permanent
magnet. If a sheet of glass or paper is placed over the steel or
FIG. 77. — MAGNETIC INDUCTION.
iron magnets and iron filings are sprinkled on its surface, the parti-
cles will arrange themselves in the direction of the lines of mag-
netic force extending far beyond the ends of the magnets and show-
ing by these curved lines of force the strains and stresses set up in
the surrounding space.
An apparatus for detecting and determining the direction of
MUTUAL INDUCTION.
81
an induced current is shown in Fig. 78. The circuit A includes
the battery 1 and the key 2 ; a second circuit B is so arranged that
FIG. 78. — INDUCED CURRENTS.
a part of its conductor is parallel with a portion of the circuit A.
In the circuit B is placed a galvanometer or telephone receiver, 3.
Now, if the key 2 is made to close the circuit A, and the current
flows in the direction of the arrow, then a momentary current will
be set up in B in the opposite direction, and when the current A
is broken a second momentary current will flow in the reverse
direction in B. This is due to the fact that on closing the circuit
A it is instantly surrounded by electricity in rotation or curved
magnetic lines spreading out in circles or tubes of force, as shown
in Fig, 79, some of which are large enough to inclose the coil B;
FIG. 79. — MAGNETIC LINES OP FORCE.
at the instant the lines from the first circuit thread through
the second coil an . e. m. f . proportional to the rate at which
they link with the second circuit B causes the momentary
current to be set up or induced. If the circuit is composed of
many turns of wire instead of a single conductor, and again if the
circuits are enlarged, the effective distance at which the currents
will be induced is proportionately increased. This is the method
82 WIRELESS TELEGRAPHY.
by which Sir William Preece was enabled to obtain indications at a
distance of eight miles, and was the method he was engaged upon
when Marconi succeeded in interesting him in his spark-gap and
coherer system.
The practical applications of electro-magnetic induction have
not been in the extension of the distance between the inducing and
the induced currents, but rather in their proper relations, as in the
case of transformers and induction coils. Another phase of electro-
magnetic induction is called into action when a soft iron core is
inserted in a coil of wire; in this case it will be magnetized by the
magnetic lines of force. The degree to which the iron will become
magnetic is termed its permeability; new properties are now
acquired through the result of this combination, i.e., an iron core
inserted in a magnetic field causes the lines of force to be greatly
intensified and the inductance produced by the turns of wire acting
on each other, as well as the mutual induction exerted by one coil
of wire on another, especially if the secondary coil consists of many
turns, is greatly increased.
PRIMARY AND SECONDARY CURRENTS. — The coil shown in Fig.
80 is one constructed by Faraday, and is the basis of the modern
induction coil, although the evolution
A. A " B.Ek' of the latter was more directly due to
Henry than to Faraday. The pri-
mary winding, AA, is formed of wire
FIG. SO.-FIRST INDUCTION COIL. of large cross-section, and the second-
ondary coil BB of wire of small
cross-section well insulated, and a soft iron core, C; the rela-
tive values of the e. m. f. impressed on the inductor or primary
coil and that produced in the secondary coil is called the ratio
of transformation. This ratio is directly proportional to the
number of turns of the inductor and secondary, except for a very
small loss in transformation ; therefore the energy at the terminals
of a secondary coil is very nearly equal to that impressed on the
primary circuit. • As an illustration, suppose the number of turns
on the secondary coil to be 1,000, and that on the primary 10,
then the increase in e. m. f. is 100 times that of the primary or
inductor, but the current or quantity of electricity will be pro-
portionately less. This ratio is called the coefficient of transforma-
tion.
MUTUAL INDUCTION.
83
THEORY OF THE INDUCTION COIL. — In treating of the several
elementary principles involved in the action of induction coils, the
effect of the magnetic field will be considered first.
ELECTRO-MAGNETIC INTENSITY. — •
In the inductor, which is a simple sole-
noid or helix, with an air core, repre-
sented in longitudinal section, Fig. 81,
i i
i i
i i i
i i
i i
i i
I I
I I
i i
the current flowing through a single
FIG. 81.— THE INDUCTOR.
turn of the coil induces at its centre a
magnetic field which may be thus ex-
pressed :
_ 2irl
' 10r
where / is the strength of the current in amperes and r the radius
of the core. In a long inductor the magnetic field within it is uni-
form except near the ends, and its intensity is
10
where n is the number of turns in the inductor per unit of its
length. This is the intensity of the magnetizing force or the
number of lines per unit of area that exist at any point, and is
represented by H.
PERMEABILITY. — Iron possesses the essential property for the
formation of the lines of magnetic force; it is therefore desirable
that soft iron cores be employed in induction coils to obtain the
maximum effect of magnetization.
The number of lines of force per
square cm. in the core is repre-
sented by B. The flow of mag-
netic lines of force is concen-
trated in the iron core, as shown
in Fig. 82. Since there is a very
great difference in the degree to
which various substances are susceptible to magnetization, air has
been taken as the standard or unit. The ratio of the magnetization
produced to the magnetizing force is represented by /w , that is,
FIG. 82. — MAGNETIC LINES IN CORE.
/i is called the permeability of the substance. Non-magnetic metals
and insulators are considered to have practically the permeability
84
WIRELESS TELEGRAPHY.
of air. Iron possesses a permeability 100 to 10,000 times greater
than that of air. As the magnetization of the core increases, its
permeability decreases so that a core may soon be completely
saturated with magnetism and additional magnetizing force will
have no further effect. In soft iron the limit of magnetic satura-
tion is about 60,000 lines of force per square cm. of cross-sectional
area.
HYSTERESIS AND EDDY CURRENTS. — When the currents of
an inductor are operated intermittently as by an interrupter of
an induction coil there is a retardation or lagging of the mag-
netizing and demagnetizing effects in the iron core due to molecular
stress; this is called hysteresis, and Ewing1 has found that the
permeability of an iron core is greater when the magnetizing force
is decreasing than when it is increasing, and thus some work must
be done, and this takes the form of heat; the curve, Fig. 83, indi-
cates this difference.
MUTUAL INDUCTION. — The total induction developed in a sec-
ondary composed of a single turn of wire wound on a closed mag-
netic circuit, as shown in Fig. 84, is (see Lodge2) independent of
N
FIG. 83. — HYSTERESIS CURVE.
FIG. 84. — MUTUAL, INDUCTION.
its size or form ; if the secondary is wound with ri turns of wire the
total induction is, of course, ri times this. The total induction $ , or
the number of lines of force cutting the secondary coil is equal to
AI
10
where ft is the permeability of the core, ri the number of turns of
wire in the primary, A the area of the cross-section of the primary
^wing, On the Magnetization of Iron in Strong Fields. Proceedings
Royal Society, March 24, 1887.
"Lodge's Modern Views of Electricity, Page 389.
MUTUAL INDUCTION. 85
in square centimeters, / the current in amperes, and Z the length.
of the primary coil in centimeters. This formula indicates that the
induction is mutually reactive, and may be simply expressed by
MI, the mutual induction between the primary and secondary
coils being represented by M, or
When an alternating or interrupted current flows in the primary
an e. m. f. is produced in the secondary proportional to the rate
at which the lines link with it from the primary thus,
d4>
e = dt'
and the potential e of the induced current in the secondary coil de-
pends on two factors, namely, the number of turns of wire in the
secondary and the rate of alternation or interruption, of the current
in the primary, or,
d* _ ._ dl _ 4imn'uA, dl
l=dt~ MdT -- ioT~ dt'
These are the fundamental principles underlying the construction
of transformers, and it is evident that as high a potential as de-
sired may be obtained by increasing the number of turns of wire
on the secondary.
FUNCTION OF THE CONDENSER. — The differentiating feature of
induction coils from those termed transformers lies in the employ-
ment of an interrupted current and a condenser in shunt with the
make and break device. The theory of induction coils having these
additional factors is quite complicated, involving new and complex
phenomena, which render the construction of coils from predeter-
mined calculations exceedingly difficult, if not, indeed, impossible.
Fig. 85 shows diagrammatically an induction
p j coil in which an interrupter is connected in
| — » i — I series with the primary winding and a con-
denser in shunt with the interrupter; the
' — \AAAA/WVV^ — ' inductance of the primary coil is represented
r~~\/\/\/\/^ _ ky ^i, the inductance of the secondary by L2,
Q the e. m. f. by E, the capacity of the con-
I. j ••* denser around the make and break by C^.
E • i ~^» ~
The object of the condenser is to produce a
^J greater difference of potential at the ter-
R°' So7T0)EiL.lNDUC" niinals PPf by permitting the primary cur-
rent to charge the condenser while the break
is taking place at the interrupter X; the more quickly the break
86
WIRELESS TELEGRAPHY.
takes place the smaller the capacity of the condenser C may be.
Lord Bayleigh has shown1 that if the primary circuit is severed by
a pistol-shot, the conditions approach- very closely the ideal break,
i.e., absolute instantaneousness, and when this ideal point is
reached the condenser may be eliminated entirely, as there is no
time for the potential of the primary to rise to a value where
it produces an abnormal spark, in which case the current, instead
of being broken, is still conducted across the gap by the rarefaction
of the air due to the heating effect of the spark itself. When these
conditions prevail the current is prevented from dropping from its
maximum to its minimum value in the shortest possible time and
the potential difference in the secondary coil is likewise diminished.
In all interrupters the period required to effect the break i&
exceedingly large, compared with zero, whether they are of the
vibrating, turbine or electrolytic type and a condenser of the proper
proportions is a necessity. Dr. James E. Ives has shown2 that
when the primary circuit is thus slowly broken the current in the
FIG. 86. — OSCILLATING CURRENT DISCHARGE.
FIQ. 87. — CONDENSER DISCHARGE IN THE PRIMARY CIRCUIT.
primary becomes alternating, as indicated in the curve, Fig. 86, as a
resultant alternating current action of the condenser. Fig. 87 is the
discharge curve of a direct current through the primary circuit fol-
lowed by the oscillatory discharge of the condenser; the period of
1 Philosophical Magazine, Vol. II., 1901, page 581.
2Ives, Physical Review, vol. 15, 1902.
MUTUAL INDUCTION. 87
alternation of the current in the primary circuit may be ascertained
by the formula,
The capacity should be reduced to as small a value as will prevent
excessive sparking ; if a greater capacity is employed than is needed
to fulfill this requirement the secondary spark will be diminished
and its efficiency decreased instead of increased. The optimum
capacity, as Johnson has termed the capacity giving the longest
spark, depends chiefly on the inductance and resistance of the
primary coil. The potential difference of the secondary coil de-
pends on the mutual inductance of the primary and secondary
coils and the relative values of capacities of the primary and sec-
ondary coils ; the primary capacity is the capacity of the condenser,
and the secondary has a distributed capacity resulting from the
turns of wire wound closely together.
Now let Y2 equal the potential of the secondary I0, the initial
primary current, M the mutual inductance of the primary and
secondary, C2 the distributed capacity of the secondary, Lx the
inductance of the primary coil, L2 the inductance of the secondary
coil, and Cj the capacity of the condenser, then the potential at
the terminals of the secondary may be found by the equation
In this equation the damping factor due to the resistance of the
coils is neglected. In the primary, as well as in the secondary coil, os-
cillating currents are set up, having a period in the primary given by
T^aryT^d,
and in the secondary by
The distributed capacity of the secondary is so small that it
may be neglected. The expression for the secondary potential then
becomes
t
Again, in properly constructed coils practically all the magnetic
lines of force of the primary cut the secondary when the primary
circuit is interrupted and
and the equation reduces to
88
WIRELESS TELEGRAPHY.
= In J^sin
which is the difference of potential at the terminals of the secondary ;
it is this factor upon which the length of the disruptive discharge
depends. Its maximum value is given by
V3max=I0^^
It is obvious, therefore, that the maximum potential difference
of the secondary is the resultant of (a) the value of the current in
the primary before interruption, (b) the inductance of the second-
ary coil, and (c) the capacity of the condenser. The potential dif-
ference of the secondary varies directly as the initial primary cur-
rent, as the square root of the inductance of the secondary and as
the square root of the reciprocal of the primary capacity. In order
to ascertain the maximum difference of potential of a coil of any
;size it is only necessary to know the initial primary current I0, the
inductance of the secondary coil L2, and the capacity of the con-
denser around the break C1? as indicated by the formula last given.
Klingelfuss has deduced the following laws, which hold for coils
of all sizes up to 100 cm. spark-length1: (a) the length of the dis-
ruptive discharge is directly proportional to the number of turns
of wire on the secondary coil; (b) the e. m. f. induced in the
primary is proportional to the primary current; and (c) the
e. m. f. induced in the secondary is likewise proportional to the
primary current. In coils having iron cores the permeability and
FIG. 88.— STRAIGHT CORE COIL.
consequently the inductance vary with the strength of the current ;
the inductance may be determined by ascertaining its value with a
email current and then with a large current, and taking the mean
JAnnalen der Physik, 5: p. 837, 1901.
MUTUAL INDUCTION.
8S>
value as the normal. Coils of various forms have been experi-
mented with, but those shown in Figs. 88 and 89 have been found
FIG. 89. — HORSESHOE TYPE OF COIL.
to be the most efficient. Klingelfuss in testing the relative values of
varying number of turns of wire on the secondary coil obtained the
curves shown in Fig. 90 ; I is the curve obtained with the horseshoe
ICO
90
80
III
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150
Turns (thousands)
Fio. 90. — EFFECT OF VARYING SECONDARY TURNS.
type of coil; II the results for a straight coil with a core of large
cross-section; curve III was obtained with a straight coil having a
core with a square cross-section, and IV by a large coil giving a
45 cm. spark. From these curves plotted by Klingelfuss it appears
that the horseshoe type of coil is the most efficient, but is not
90 WIRELESS TELEGRAPH.
practicable for high potentials, as the sparks take place across the
air-gap of the magnet.
The curves, Fig. 91, are due to Ives, and show that when the
iron in the core is increased the potential of the secondary rises very
70
CO
50
300 400
Number of wires
Fio. 91.— EFFBCT OP IRON IN CORE.
rapidly at first and more slowly afterward. The curves, Fig. 92,
showing the effect of varying the capacity around the break, are by
Mizuno, and demonstrate graphically the value of increasing .the
capacity of the condenser to the critical point of optimum capacity,
when the disruptive discharge is of maximum length, and that any
increase of capacity above this value tends to decrease the spark-
length. The phenomenon of distributed capacity of the secondary
coil is difficult of elucidation, as well as the law of the break of
the primary current, but while these and other obscure factors are
yet without the pale of mathematics, the theory of the induction
coil with all its complexities are fairly well evolved, and from the
foregoing formulae and equations the determination of the elements
MUTUAL INDUCTION.
91
.2 .3 .i .5 .6 .7 .8 .9 .10
Capacity (Microfarads,)
FIG. 92. — EFFECT OF CAPACITY ABOUND BREAK.
and constants of induction coils may be obtained with a reasonable
degree of accuracy.
CHAPTEE IX.
INDUCTION COILS.
HISTORICAL.
While Faraday's ring is the prototype of the modern induction
coil, the development of the latter seems to have been more directly
due to Henry's flat spirals. Sturgeon made some experiments with
coils with and without iron cores in 1836, and in the same year
an important advance was made by Prof. S. S. Page, of Wash-
ington, when he interrupted the battery circuit by a rapidly
revolving spur wheel,1 and later made and broke the circuit by
drawing one end of the battery wire over a file. The primary
and secondary coils of Henry and Page were made continuous,
that is, a thick wire was first wound into a helix, and then sol-
dered to one terminal of this was a long thin secondary. Callan,
in 1836, describes the construction of his coil as being made
of two separate insulated wires, one thick and the other thin,
wound on an iron core together, but the peculiar construction lies in
the fact that the secondary or thin wire was joined to the end of the
thick wire, so that they formed one circuit, as in the case of Henry
and Page. Callan also devised an "electro-magnetic repeater," or
"vibrating contact breaker," for interrupting the circuit. Sturgeon,
the inventor of the electro-magnet, investigated the influence of
electrical currents on soft iron as regards the thickness of the metal
requisite for the full display of magnetic action. Sturgeon ap-
plied to his coil a make and break arrangement consisting of a wire
dipping into a cup of mercury and operated by a revolving cam and
lever producing 36 breaks per second ; this he subsequently changed
for a disk and obtained 540 breaks per second; he then placed a
solid iron core in the coil and obtained powerful shocks. After
some trials he substituted a bundle of fine iron wires for the solid
core and obtained much better results. Bachhoffer also noted the
'Silliman's American Journal of Science, October, 1836.
• 92
INDUCTION COILS. 93
same conditions. Sturgeon's coil was an advance over those made at
that time, and the general form he gave it has been retained to
the present day.
Callan, in a paper dated September 11, 1837, and printed in
Sturgeon's Annals of Electricity, says: "In making electro-mag-
nets (coils) which are to be connected for the purpose of obtaining
increased electric intensity care must be taken not to solder the
thin to the thick wire, but to leave both ends of the wire projecting."
In a note he recommends that for lecture purposes the thick wire
and the thin wire should be wound on separate spools, so to Callan
we owe, not only this form, but an induction coil having a pri-
mary of thick wire and a secondary of fine wire. In this year
Barker designed a make and break device in the form of a star
arranged so that the projections dipped into a vessel of mercury,
and this has ever since retained the name of Barker's wheel. About
this time Bachhoffer states that he applied to his coil a self-acting
contact-breaker, and this is the earliest reference to an automatic
interrupter. Callan advanced the idea of connecting the secondary
circuits of a number of coils in parallel and Fleming credits him
with the knowledge at that date of adding up the electro-motive
forces of a number of distinct coils.1 In a paper of 1837 Callan
contributed another great improvement in the method of construct-
ing induction coils; this consisted of increasing the insulation of
the secondary by drawing the wire just prior to winding through a
hot bath of melted resin and beeswax, which mode is still in use.
To Poggendorf we are indebted for the invaluable suggestion of
winding a large number of thin flat coils, after insulating them,
so that there could be no great difference of potential between the
immediate coils, and then connecting them in series.
Callan constructed one of the largest coils, up to the advent of
wireless telegraphy, ever built. It was completed in 1863 and gave
a spark of 15 inches in length. It is still preserved in Maynooth
College, England. In 1837 Page invented his rocking-magnet in-
terruptor. By many he is credited with the discovery of the di-
vided coil. In 1838 he constructed a most efficient coil operated by
an automatic make and break formed of a vibrating spring dipping
in a cup of mercury. He noted the untoward effect of the spark
at the point of break, due to the continued passage of the current
1 Fleming's Alternate Current Transformer, Vol. II.
94 WIRELESS TELEGRAPHY.
caused by the mercury vapor, and remedied this by flowing the
surface of the mercury with oil. Page was likewise the first physicist
to show that the secondary discharge of an induction coil was simi-
lar in every respect to a static discharge, and that electrostatic ten-
sions could be obtained, Ley den jars charged, the leaves of an elec-
troscope diverged and many other phenomena produced heretofore
observed only with electrostatic machines. Page also noted that
the spark could be lengthened by heating the air between the oscil-
lator balls, and obtained a spark 4% inches in length with a dis-
charge giving normally a maximum spark of ^r inch in the air. He
observed also the phenomenon that the spark of a primary circuit,
when broken, was extinguished by introducing the terminals be-
tween the poles of a powerful magnet when the spark was blown
out with a loud report.
Wagner and Neef improved upon Page's mercurial break in
1840 by designing the now familiar vibrating armature with plati-
num contacts. With this invention the induction coil was prac-
tically completed with the exception of the condenser. In 1851
Ruhmkorff greatly improved the efficiency of the coils by carefully
insulating the secondary from the primary by means of a glass tube
and with glass disks at either end to hold the wire in place. He
provided also the commutator for reversing the current, and to-
gether with his improvements of the vibrating interrupter he be-
came famous as a maker of induction coils, and to-day his name
stands as a symbol for high-tension coils. The last important and
one of the greatest improvements was made by Fizeau1 by the addi-
tion of the condenser. Ruhmkorff at once took up the work and
designed condensers especially adapted for the purpose and made
them with carefully proportioned dimensions. Ruhmkorff made his
condensers of oiled silk or paper with intervening leaves of tinfoil.
The condenser thus formed was placed in the base of the coils and the
opposite terminals connected to the opposite posts of the inter-
rupter. In 1867 Ruhmkorff constructed his chef-d'oeuvre, a coil
giving sparks 40 cm. in length. M. Jean, an amateur coil builder,
devised a method for securing better insulation in 1854. This con-
sisted in immersing the whole coil in a liquid insulator such as
oil or turpentine. He also baked and dried the coil to eliminate
any remaining moisture previous to immersion and performed the
whole process in a vacuum, thus avoiding contact with the air in
lComptes Rendus, 1853. Fizeau.
INDUCTION COILti. 95
the transfer of the coil to the oil. Taking advantage of all these
improvements in the building of coils, Alfred Apps, a London
maker, constructed the famous Spottiswoode coil1 giving a spark
42 inches in length.
PRACTICAL.
In the construction of induction coils for practical wireless
telegraphy a heavy and continuous secondary discharge is of prime
importance. Induction coils for this class of work should be con-
structed upon lines somewhat different from those usually followed
in ordinary coils, that is to say, they need not be wound to obtain
excessively high potentials, and the secondary coil should exercise
but a slight reaction on the magnetic lines of force, thus offering
but little opposing influence to the primary current.
To obtain these desirable features the inductor or primary coil
is made quite long and the secondary coil is proportionately shorter
and is wound with wire having a much larger cross-section than an
ordinary coil, thereby decreasing the losses by ohmic resistance to a
minimum, since every turn of wire not absolutely required to obtain
potential adds to the total resistance ; the use of wire of large cross-
section also reduces to a minimum the heating due to alternating
secondary currents. The secondary coil should be doubly insu-
lated, thus strengthening the weakest points of the induction coil
and rendering its disruption under the heavy demands of com-
mercial wireless telegraph practice practically impossible.
CORES. — The core of an induction coil should be made of care-
fully annealed Swedish soft iron wires, preferably of No. 18, 20, or
22 B. & S. gauge, cut into suitable lengths and bound into a compact
bundle. It has been found that by increasing the diameter of the
core in proportion to its length a greater frequency of interruption
is possible, which is a great advantage when an electrolytic inter-
i uptor is employed in connection with it, since the B H curves are
described with little retardation even when the frequency of inter-
ruption reaches a value of 10,000 per minute; this is due to the de-
crease of resistance offered by a coil of large cross-section to the flow
of the magnetic lines of force through it. This magnetic reluctance,
1 Philosophical Magazine, January, 1887, p. 30.
96 WIRELESS TELEGRAPHY.
as it is termed, is the divisor where the magneto-motive force is
the dividend, and the quotient is the magnetic flux, or it may be ex-
pressed thus :
The magnetic flux
. = Magneto-motive force.
The reluctance.
The core of the coil should be long and extend from two to
six or eight inches beyond the secondary; by this arrangement the
number of lines of magnetic force cutting a turn of the secondary
is greater at the middle than at the ends, and therefore less wire
may be employed in the secondary.1
PRIMARY COILS. — In large coils the inductance between the
local turns of wire is the cause of excessive sparking at the
interrupter. To overcome this objectionable feature, the primary
coil is made up of a number of turns of small wires, the multiple
winding is equal in conductivity to a single wire of large diameter.
This gives better results in virtue of a closer winding of the wire
on the core. The inductor or primary coil gives the best inductive
effects when wound in two layers on the coil. Double-covered
cotton or silk magnet wire may be used, and the size depends on
the length of the sparks and the kind of discharge desired. In
wireless telegraphy where thick discharges are required a corre-
spondingly heavy current must flow through the inductor, and
thus a wire of large cross-section should be used. The strength
of the disruptive discharge is subject very largely to the degree
of magnetization of the coil, and this, by the number of turns of
wire on the inductor, providing they are in close proximity to the
coils, in virtue of the law of ampere turns, which, simply stated,
is that a current flowing through a number of turns of wire is
equal to the number of amperes flowing through a single turn
multiplied by the number of turns of wire.
In the construction of inductors it is desirable to minimize the
inductance of the turns, since the effect of this local self-induction
is to produce a retardation of the primary current, therefore wire of
large cross-section is employed together with a double layer of
wire; if the wire is too large difficulty may be expected in the
nature of excessive sparking at the interrupter. For wireless tele-
iphysical Review Ives Vol. XIV., 1902
INDUCTION COILS. 97
graph transmitters/ makers of coils have found the following sizes
of wire suitable for the inductors:
c,. e -i • No. of wire.
Size of coils m spark length B & S Gauge
!/2 inch to 1 inch No. 16
1 inch to 2 inches No. 15
2 inches to 4 inches No. 14
4 inches to 8 inches No. 13
8 inches to 12 inches No. 12
The inductor should be wound to occupy nearly the entire
length of the coil, and then treated to a coat of insulation.
SECONDARY COILS. — To obtain a heavy and rapid disruptive dis-
charge the secondary coil should be wound with wire having
at least fifty per cent, greater cross-section than in ordinary types
of induction coils found in the open market, yet the number of
turns of wire should remain the same, and to increase the output
of a coil thus constructed so that it will give its maximum efficiency
the secondary coil should be wound with the least number of turns
of wire possible and yet be capable of producing a given length of
spark, since every additional turn of wire not absolutely necessary
increases its resistance and decreases the amperage of the secondary
current without proportionately increasing the length of the spark.
Coils for wireless telegraphy are, in consequence, larger than the
usual types; but this feature is compensated for in virtue of its
giving heavy, white and powerful discharges which are capable of
setting up in the radiator system oscillatory currents of great
power.
In order to obtain the proper distribution of wire in the sec-
ondary the best method is to ascertain the spark length of single
coils made of a few turns of wire and placed at intervals along the
core and in the magnetic field of the. inductor ; curves may then be
plotted which will give fairly accurate determinations of the proper
amount and distribution of wire. The secondaries of induction
coils giving 2 inch sparks and under may be wound of continuous
wire, layer upon layer, until the proper amount of wire per given
Bpark-length is used ; the cheaper coils to be found in the market are
built up in this manner. But for effective work in wireless teleg-
98 WIRELESS TELEGRAPHY.
raphy the winding of the secondary must be composed of sectional
disks. In coils of 1 inch spark-length two or more sections may be
employed, and these sections should decrease in thickness, increase
in diameter and be added to in number as the size of the coil in-
creases. Sectional disks iV inch in thickness are the most suitable
for coils giving sparks 12 to 18 inches in length.
In winding these sections the wire is drawn through a melted
insulating compound composed of three parts of resin and one
part of beeswax ; the silk insulated magnet wire, with this additional
insulating medium still hot upon it, is reeled into a thin flat coil
between two brass disks having planed surfaces and carefully ad-
justed so that each surface shall have the same thickness and
c^pproximately the same amount of wire on it. The sectional disks.
FIG. 93. — CONNECTING DISKS OF SECONDARY. FIG. 94. — CONNECTING TERMINALS OF
SECONDARY DISKS.
are then dried and partially assembled when they are connected in
series, as shown in Fig. 93, where the outer terminal of one section
is connected with the inner terminal of the next one. A more recent
practice is to connect the outer terminals of the first two sections
together and then the inner terminals of the next two, as shown in
Fig. 94; in the case illustrated in Fig. 93 the terminal of one coil
is brought down between the sections in order to make connection
with the inner terminal of the next section to it, and this has a
tendency to produce short-circuiting and sparking between the
individual sections. This is obviated in the latter method, the cur-
rent flowing in the same direction through all of the sectional disks.
Some makers of induction coils increase the number of turns
of wire in the sections which are to occupy the middle of the core,
so that it will be much larger and the amount of wire much
INDUCTION COILS. 99
greater than at the ends,1 as shown in Fig. 95. This arrangement
brings the greatest number of turns in a position where the mag-
netic field is at its maximum value. In ordinary induction coils
where a long, thin disruptive discharge is desired, the secondary
coil is wound with No. 36 to 40 B. & S. magnet wire, but in wire-
less telegraphy where a heavy spark is essential No. 30 to 34 wire
is used. The amount of wire per inch spark for coils up to 6 inches
of No. 34 wire is approximately ll/2 pounds ; for coils larger than 6
inches it is about a pound.
INSULATION. — Where heavy disruptive discharges are required,
the insulation of the secondary coil must be carefully considered.
It is of prime importance that all the air is removed from the
spaces between the turns of wire in the sectional disks and from
FIG. 95. — CONVEX SECONDARY WINDING.
the interspaces between the sections themselves after assembling.
These minute air bubbles weaken a coil and diminish its efficiency,
and may in time cause its total disruption, due to electrostatic
bombardment of rapidly alternating currents at high potential
which develop heat.
To prevent these untoward effects, manufacturers construct what
is termed a vacuum secondary; the sectionally wound disks are
dried before removal from the winding machine, and after being
assembled they are immersed in a melted insulating compound of
resin and beeswax; the air is then thoroughly exhausted; when
removed the coil is inclosed in a solid mass of air and moisture-
proof insulation. Oil is of course the ideal insulation, but it adds
bulk to the coil, and there is always danger of leakage, while the
process described gives excellent satisfaction and has been adopted
by all the leading manufacturers.
Electricity: Its Theory, Sources and Application. Sprague.
100 WIRELESS TELEGRAPHY.
ASSEMBLY OF PARTS. — After the coil is properly mounted an
interrupter and a condenser are necessary adjuncts to complete the
equipment. The interrupter should be constructed to operate
smoothly and uniformly without regard to the variability of the
disruptive discharge while in action. The condenser should be
adjustable so that sparking of the interrupter contacts may be
reduced to a minimum, in accordance with the laws of capacity and
inductance already elucidated. Interlocking switches are now
placed on large coils, which prevent short circuits, etc. By their use
it is impossible for the current to flow through the primary until
the interrupter is in operation.
SOURCES OF ELECTRO-MOTIVE FORCE. — Induction coils may be
operated by primary cells, storage batteries, or by a direct 110-volt
current. In wireless telegraph practice it is preferable to operate
coils from 110-volt circuits where practicable, as the increased
energy gives a heavier discharge, and therefore more powerful oscil-
lations are set up in the radiator. Where primary batteries are
employed a large excess current must be provided, or the discharge
will be enfeebled and the coil, whatever its make and rating, will
be inefficient. It is not advisable to operate coils on 220-volt cir-
cuits, since the reaction on the primary is dangerous alike to the
coil and the operator. Where a 220-volt direct current is available
a small motor-generator may be installed; that is to say, a direct
current motor operating on a 220-volt circuit may be directly con-
nected to a 110-volt dynamo, which supplies energy to the coil, or a
motor-generator answering the same purpose may be used. A motor
with two windings on its armature, one to take the current at 220
or 500 volts and the other to generate a current of 15 amperes at 20
volts, may also be used. An alternating current cannot be employed
directly to operate an induction coil, for the reason that the rate of
alternation of the current has a time constant too high to give-
efficient disruptive discharges without heating the coil. Alternating
currents may be used, however, by utilizing in the circuit a Cald-
well liquid interruptor or designing the induction coil so that a
Grisson converter may be introduced.
SELECTION AND CARE OF A COIL. — In ordering induction coils
for wireless telegraphy there are a number of factors to be taken
into consideration. Coils are rated by the length of spark they
give, and the heavier the discharge the whiter the spark appears. The
rating of an induction coil should be made when the coil is operated
INDUCTION COILS. 101
normally, and not by the mere length of a single discharge. A coil
working with a current of 15 amperes at 20 volts = 300 watts
should completely fill a spark-gap one inch long between terminals
made of i/^-inch disks. It is often convenient to know the polarity
of the secondary discharge. This may be easily ascertained, since
the positive terminal is always cold, whilst the negative terminal
is hot when the coil is in action. If a Geissler tube is attached to
the terminals the positive glows with a purplish red light and the
negative with a bluish violet light.
FIG. 96. — ORDINARY INDUCTION COIL.
The proper care must be taken of an induction coil to get the
best results, and unless handled with the consideration usually
bestowed on other fine mechanical or electrical appliances the re-
sults will not be satisfactory. The interrupter should be kept clean
and the surfaces of the platinum contacts smooth and parallel with
each other; when an adjustable condenser is employed care must
be exercised to obtain the proper capacity. If too large or too small
a capacity is used the performance of the interruptor will be ren-
dered variable, and excessive sparking will result. One of the most
common causes of failure in the operation of coils is, however,
directly due to insufficient current; if batteries are utilized as the
102
WIRELESS TELEGRAPHY.
source of current it is of vital importance that there should be
a very large excess, for effective discharges are only obtained by
currents of large amperage.
TYPES OF INDUCTION COILS. — In Fig. 96 is shown a 2" induction
coil the secondary of which is formed by winding a continuous wire
in several layers around the primary. The layers are insulated from
each other by paraffine paper. Coils constructed on this simple plan
are made in sizes giving from 14" spark to a 2" spark. These coils
FIG. 97. — MODERN INDUCTION COIL.
are equipped with single vibrating spring interrupters and paper
condensers; they give quite satisfactory results for experimental
work provided they are carefully handled. By way of comparison,
Fig. 97, illustrating a 2" coil of modern design, is given; in this the
secondary is built up of disks and insulated with wax and rosin.
The interruptor is of the double spring vibrating type and the break
is shunted with a mica condenser.
A ten-inch coil built by Foote, Pierson & Co., is shown in Fig.
98. This is equipped with all the latest modern improvements, in-
suring successful operation under strenuous conditions; it includes
INDUCTION COILS. 103
an independent multiple interrupter, interlocking switch, safety-
fuse block, adjustable mica condenser, special switches, posts for
electrolytic interrupters and a series parallel arrangement of the
inductor. Fig.' 99 pictures the exterior appearance of the coil used
in the Lodge-Muirhead system, the construction of which is similar
to that indicated in the preceding portions of this chapter.
The Kinraide coil consists of two separate secondaries with
their primaries connected in series. Each secondary has a high and
FIG. 98. — FOOTE-PIERSON DELTA COIL.
low potential terminal resulting from the position and method of
winding the inductors. The primary of each side is wound outside
the secondary winding. The object of this is to overcome the
tendency of the secondary to discharge into the primary coil. Fig.
100 represents the coil photographically. The Braun-Siemens and
Halske coil, Fig. 101, follows the specifications given for properly
designed coils for heavy service, the secondary being wound with
wire having 50 per cent, greater cross section, with double the in-
sulation of ordinary coils. The physical characteristics of the Slaby-
Arco coils are practically the same as those of the Braun type. In
104
WIRELESS TELEGRAPHY.
ITig. 102 a reproduction of a coil designed by Fessenden is given.
It will be observed that the core and primary extends on either side
~ -B. Ink-
FlG. 99. LODGE-MUIRHEAD COIL.
FIG. 100. — THE KINRAIDE COIL.
of the secondary to a distance several times the length of the latter.
It has been shown by experiment that additional secondary coils
INDUCTION COILS.
105
near the ends of the core enhanced to a very small extent the output
of the current of the secondary.
FIG. 101. — BRATJN-SIEMENS AND HALSKE COIL.
The largest induction coils ever made for wireless telegraphy
are shown in Fig. 103. Two of these immense coils were built by
FIG. 102. — FESSENDEN LONG CORE COIL.
Queen & Co., for the Japanese Government. The core of the in-
ductor is formed of iron wires, making a bundle measuring 5 inches
in diameter, having a length of four feet and weighing 200 pounds.
106
WIRELESS TELEGRAPHY.
This core projects 12 inches beyond either end of the secondary, the
latter being divided into two parts, built up of sectional disks and
containing 100 miles of fine and carefully insulated magnet wire;
when completed the outside of the coils measured 15 inches. The
interruptor is driven by an electric motor, actuating heavy pieces of
FIG. 103. — QUEEN METER SPARK COIL.
platinum which breaks under oil, -while a variable mica condenser is
provided to cut down any undue sparking. Either a 110 volt d. c.
may be used, or a 25 volt, 20 ampere current from a storage battery
when a maximum spark of 42 inches in length or an exceedingly
heavy disruptive discharge may be obtained.
CHAPTER X.
INTERRUPTORS.
PRACTICAL.
The evolution of the modern high-class induction coi) has called
forth much effort and ingenuity in providing a simple method for
making and breaking the primary circuit with precision and rapid-
FIG. 104. — SIMPLE VIBRATING INTERRUPTOR.
ity. The requirements of a good interruptor are (1) a break ap-
proaching as nearly as possible the ideal, i.e., absolute instantaneous-
ness, (2) high-speed interruptions, (3) arbitrary variability of
frequency of make and break at will of the operator, (4) inde-
pendence of action of the current flowing through the inductor, and
(5) capability of carrying large currents. Of interrupters there
are four general classes, (a) mechanical vibrating, (b) mechanical
107
108 WIRELESS TELEGRAPHY.
rotating, (c) mercurial turbine, and (d) electrolytic. As to the
best type of interrupter there is a wide difference of opinion everi
among experts, but the mechanical vibrating is the simplest type,
easy to keep clean and in adjustment, and therefore extremely
suitable for all ordinary classes of work. Where the highest effi-
ciency is desired, as in wireless telegraphy, the mercury turbine or
electrolytic types are especially serviceable, and since trained
FIG. 105. — CONDENSER SHTJNTED AROUND BREAK.
operators are in charge, the care and manipulation of these more
complex devices become a secondary consideration.
SIMPLE VIBRATING INTERRUPTOR. — In this type of interrupter
the make and break is accomplished by means of a vibrating spring,
one end of which is held stationary, while its free end carries an
armature magnetically operated by the core of the coil, as shown in
Fig. 104. This vibrator is connected in series with the primary
coil and the battery, and is so arranged that when no current is
flowing through the circuit the spring carrying a movable con-
tact point closes the circuit through a stationary contact point;
when the current is permitted to flow through the circuit the core of
INTERRUPTORS.
109
the coil is magnetized and attracts the armature, causing the cir-
cuit to be broken when the elasticity of the spring pulls the points
into contact, closing the circuit again. A condenser is shunted
around the break, as per diagram, Fig. 105. This type, known as the
Neff hammer interruptor, has been employed on large coils — up to
10 and 12-inch — but is not a very satisfactory device for with-
standing the heavy strains to which it is subjected in wireless
telegraphy, although it is employed extensively by English makers
and was used by Marconi in many of his most successful tests.
FIG. 106. — DOUBLK SPRING INTEKKUPTOR.
This interrupter is almost universally used in coils up to 4 inches.
Its periodicity of interruption is variable only through a very lim-
ited range of vibration, it has a tendency to stick when heavy cur-
rents are used, and its vibrations are sinusoidal, which affects the
rate of discharge; oppositely disposed, its frequency is fairly high
and may be determined by the musical note it emits. A high or
low period of vibration can be arbitrarily given it by the maker by
employing a thick, short spring when very rapid movements are
desired, or a long, thin spring if a slower rate is necessary, thus ob-
taining the most suitable value of frequency for the operation of
the coil, the range available being from 0 to 2,500 makes and breaks
per minute.
110
WIRELESS TELEGRAPHY.
DOUBLE-CONTACT INTERRUPTOR. — This is a modified form
of the above vibrating type, but has a platinum contact on
both sides of the spring, the make taking place as the amplitude
of the spring reaches its maximum in both directions, the break as
the elasticity of the spring moves toward 0. By this means the
frequency of the interruption may be increased to 5,000 vibrations
per minute. The greatest difficulty with this form is in its sticking
propensities.
DOUBLE-SPRING INTERRUPTOR. — In all single-spring inter-
rupters the movable contact point is secured directly to the spring
FIG. 107. — INDEPENDENT INTERRUPTOR.
midway between its stationary and its free end; where heavy cur-
rents are employed the platinum contacts very often stick, due to
the fusing of the points, which on cooling become welded together,
rendering the device inoperative. In the double-spring inter-
rupter (Fig. 106) two springs are called into play, the
small one carrying a movable platinum contact, projecting
through a collar in the large one, which acts as the vibrator
spring proper. When the platinum points come in contact
with each other the large spring is not arrested in its action,
but is carried forward until it reaches its full amplitude,
thus giving the contact points the benefit of a long make ; when the
spring is returning it strikes the collar of the small spring and
breaks the contact with all its acquired momentum at full speed.
INTERRUPTORS.
Ill
per
C2Z3 I v
lt
•3.
V//////A
This is a decided improvement on the simple-spring vibrator, since
in the latter the break takes place at the instant the spring begins
to move. In the double-spring interrupter the force is sufficient
always to break the slight weld at the contact points.
INDEPENDENT INTERRUPTOR. — By the term independent it is to
be inferred that this type of vibrator is a complete device in itself,
although a subsidiary piece of apparatus of the induction coil. It
usually embodies all the improvements of the double-spring inter-
rupter, and, being operated on a shunt, it may be started or stopped
at will and the current flowing through the inductor completely
made or broken or intermittently interrupted— as the specifications
of some wireless telegraph systems
call for — as desired. Fig. 107 is a
photograph of a standard independent
interruptor, and Fig. 108 shows the
connections where an independent
vibrator, is employed ; 1 represents the
contacts for the short circuit; 2 the
interruptor magnets ; 3 the large con-
tacts for the primary circuit; 4, 41
the primary coil in two layers and
5 the source of e. m. f. Independent
interrupters are especially adapted to
operate coils on 110-volt circuits. In
the type shown a vertical rod is at-
tached to the free end of the large
vibrating spring and carries a sliding weight retained in position
by a set screw. By adjusting the weight the period of vibration
may be varied within certain limits, offering a decided advantage
in adjusting it to the requirements of wireless telegraph trans-
mission. Other features of this interruptor are as follows: its
action is independent of the heavy current flowing through the
coil, it gives a clean-cut and sharp • break, and it cannot stick.
An adjustable condenser is very often mounted on the same base
with the independent interruptor, and is an important feature
where a variable speed takes place, since different periods of inter-
ruption require capacities of different value. The magnet of the
interruptor should be especially wound for the current with which
it is to be operated. The adjustable condensers usually have a
total capacity of 4 or 5 microfarads subdivided into fifths, so that
TIG. 108. — CONNECTIONS OF INDE-
PENDENT INTERRUPTOR.
112
WIRELESS TELEGRAPHY.
a suitable value may be had for every condition which may arise
in using it in connection with the smallest or the largest of coils.
Another improvement in this type of interruptor is to design it
with two magnets arranged so that the armature and spring will
just clear the inner surfaces of the polar projections of the mag-
nets, as in Fig. 109. This gives the spring an unlimited play, so
that its full amplitude may be called into action, making it very
positive and powerful.
FIG. 109. — DOUBLE POLE INDEPENDENT INTERRUPTOR.
MECHANICAL BECIPROCATING INTERRUPTOR. — In testing the
action of interruption on the coefficients of coils experimenters
usually employ the simple and efficient method of plunging and
removing, by hand, one of the terminals of the inductor into a
vessel of mercury which is in circuit with the battery and primary
coil. The fundamental feature of a mercurial make and break was
utilized by M. Bichat in 1875, who adapted it to a reciprocating
mechanism operated by a magnet, as in Fig. 110. It consists of an
electro-magnet, Et with automatic interruptor, B, like a vibrating
bell working on a shunt circuit. The armature carries the rod Lf
to which is fastened the contact point T. The mercury is represented
INTERRUPTORS.
113
by the black space at the bottom of the vessel and is marked — ,
while the contact point forms the + terminal ; the mercury ia cov-
ered with vaseline to prevent sparking and oxidization.
UJ
FIG. 110.
MECHANICAL ROTATING INTERRUPTOR. — The mercury type of
interrupter designed by Bichat and the rotary type made by Du-
FIG. 111. — ROTATING INTERRUPTOR.
cretet are much used in France. In the latter device the recipro-
cating motion of the movable contact point is obtained by the ro-
114
WIRELESS TELEGRAPHY.
tary action of an electric motor.1 The motor, P, is mounted on an
insulated standard. The shaft Am of the armature is provided with
a cam, Ex, operating in a longitudinal slotted plate to which is
attached the rod t and the collar, T, as in Fig. Ill, in which the
platinum contact point is adjusted ; this point makes and breaks
contact with mercury in the vessel here, as in Bichat's interrupter.
Covering the mercury is a layer of
petroleum or alcohol to prevent
sparking. The interrupter has a
periodicity of 600 to 800 per min-
ute when operated by the motor.
Fig. 112 is a diagram of the inter-
ruptor. An adjusting screw, Bf
serves to raise or lower the mercury,
giving a longer or shorter period of
make, as the case may require. The
speed is governed by means of the
rheostat, R, and its ease of manipu-
lation, reliability, and sharp break
make it a serviceable device where
low-speed interruptions can be used
to advantage.
MERCURY TURBINE INTERRUP-
TOR. — The mechanical interrupters described are exceedingly easy
to manipulate, require little attention, and are always ready
for use, and for these reasons are generally supplied with induc-
tion coils for sale in the open market. In wireless telegraph
practice better results are obtained with interruptors haying a
smaller time constant, and which therefore more nearly ap-
proach instantaneousness of break. The mercury turbine is a
device of this character offering a range of interruption from
10 to 10,000 per minute, with the relative times of make and break
under the control of the operator. The cut, Fig. 113, shows the
mercury jet interrupter designed by Dr. R. H. Cunningham.2 It
consists essentially of a hollow spindle containing a steel worm, P,
revolved by a motor not shown, but belted to it by a pulley at 8.
Mercury is contained in the well below, and when the spindle is
rotated the mercury is drawn upward and forced outward through
*Comptes Rendus, Academy of Sciences, June 14, 1897.
1 Electrical World and Engineer, October 12, 1901.
FIG. 112. — SCHEME OF ROTATING
INTERRUPTOR.
INTERRUPTORS.
115
the lava-tipped- steel tubes, QQ, by centrifugal force ; the mercury
as it is thrown out impinges with great force upon oppositely dis-
posed sectors of sheet iron arranged in pairs, as shown at 7; these
sectors are connected to the terminals HHf the circuit being formed
between the sectors through the mercury jets, QQ. The corners of
the sectors are cut off at an angle, the breaks taking place as the
impinging jet passes over the portions that are cut away. The
\
FIG. 113. — MERCURY TURBINE INTERRUPTOR.
terminal rods HH may be raised, or lowered, and the length
of time required for the contact between the sector and the jet
may be varied at will. In the mercury turbine two pairs of
sectors are usually employed, which produce four breaks per revo-
lution, but three or more pairs of sectors may be used and the
number of breaks per second increased if desired.
The break in this type of interrupter is very sharp, owing to
the centrifugal velocity of the jet of mercury as it leaves the edge
of the sector, and in the Cunningham interrupter this is accentuated
to a further degree by jets of compressed air attached to the mer-
116
WIRELESS TELEGRAPHY.
cury jets QQ'} the air is compressed by two trumpet-shaped pipes,
TT, attached to the spindle Pf and as they revolve at a high
velocity an air-blast is forced out of their tips. After the mercury
has been projected against the sectors it falls back into the cavity
ready to be used again. The radial projections on the bottom of
this well or cavity prevent the rotation of the mercury. It requires
about six pounds of mercury to charge the turbine, and after it has
been in operation for a month it should be removed and the parts
cleaned by washing in a solution of bichromate of potassium. When
FIG. 114. — COOLING WORM FOR ELECTROLYTIC INTERRTTPTOR.
driven by a synchronous motor the crest of each wave flowing in the
same direction may be sheared off, and thus any induction coil may
be operated by an alternating current and unidirectional disruptive
discharges result at the spark-gap. A condenser of small capacity
should be shunted across the interrupter to obtain the best results.
ELECTROLYTIC INTERRUPTOR. — In systems, of wireless teleg-
raphy, especially those of German manufacture, the Wehnelt elec-
trolytic interrupter has met with favor, and the results attained
have been very satisfactory. Interrupters of the electrolytic type
consist of a platinum anode having a surface of approximately 4
square mm. and a lead cathode having a surface approxi-
INTERRUPTORS.
117
mating 300 square cm., both being immersed in a solution
of sulphuric acid 1 part, and water 5 parts. When these electrodes
are connected in series with the inductor and a source of e. m. f.
having a potential of 40 volts, bubbles of non-conducting gas are
formed on the terminal of the platinum anode which interrupts the
current ; the frequency of the formation and bursting of the bubbles
varies directly as the e. m. f. employed, and inversely as the area
of the platinum surface.
FIG. 115. — ELECTROLYTIC INTEKKUPTOR.
On very large coils this type of interrupter is not theoretically
efficient, since a current of 3 or 4 amperes is required, and this
causes a loss of 100 to 150 watts, due to the heating of the solution,
which if continued affects the rate of interruption, diminishes the
sharpness of the break, and sometimes results in absolute failure.
For these reasons the solution should be kept at a uniformly low
temperature, and in practice this may be accomplished by the use
of a cooling worm having a head of water flowing through it; the
general arrangement of the worm is shown in Fig. 114, and it may
be supplied from the street mains or by using a siphon of rubber
tubing. In the Braun-Siemens and Halske type of electrolytic inter-
118
WIRELESS TELEGRAPHY.
ruptor the containing vessel is swung in two concentric rings, or
gimbels so that its equilibrium may be maintained at all times, and
is especially useful for marine work, where the rolling of the boat
would affect it ; this interrupter is shown in Fig. 115. When an elec-
trolytic interrupter is employed the usual condenser shunted around
the make and break is not necessary, as the interruptor itself has a
certain inherent capacity due to electrolytic action, and termed
FIG. 116. — DOUBLE ELECTROLYTIC INTERRUPTOK.
electrolytic capacity, which is sufficient to maintain the proper
relations of the coefficients. A vent should be provided in the top
of the containing vessel and attached to a sponge dampened with
water or an alkali solution. Fig. 116 is a double electrolytic inter-
ruptor.
An alternating current may be used in connection with an
electrolytic interruptor for the negative current impulses have no
appreciable effect, while the positive impulses will electrolyze the
solution and gas bubbles will be formed as in the case of the ordi-
INTERRUPTORS. 119
nary direct current. The platinum point is, however, very rapidly
reduced when an alternating current is used, for the negative cur-
rent acts like a direct current when the platinum point is made the
cathode and the lead plate the anode, and its maintenance is there-
fore quite expensive; but where an alternating current only is
available it may, by this method, be pressed into service. In prac-
tice at least 40 volts are required to obtain good results, and the
rate of interruption is from 1,000 to 10,000 per minute.
LIQUID INTERRUPTOR. — This interrupter is due to Mr. E. W.
Caldwell and is essentially electrolytic in action.1 In this type,
FIG. 117. — LIQUID INTERRUPTOR.
Fig. 117, there are two metal electrodes immersed in a conduct-
ing solution or electrolyte; the electrodes are separated from each
other by a punctured insulated diaphragm. When in action the
current flowing through the circuit has a greater density at the
orifice of the diaphragm, with the result that a bubble is formed
which interrupts the current; the bubble then collapses, as in the
Wehnelt type, only to be formed again, disrupted, and so on. The
rapidity with which the make and break .takes place varies with
the amount of current flowing in the circuit, its inductance, size
of the orifice in the diaphragm, the depth of the electrodes in the
solution, and several other minor factors. Like other electrolytic
^Electrical Review, New York, May 3, 1899.
120
WIRELESS TELEGRAPHY.
interrupters, not less than 40 volts are required to operate it, and
an alternating current may be employed if a direct current is
not available.
ROTARY INTERRUPTOR. — In all the foregoing interruptors the
impulses in the inductor are in the same direction, and unidi-
rectional discharges result between the spark-balls connected to the
terminals of the secondary coil. Rapidly alternating currents may,
however, be produced by means of the rotary pole-changing inter-
rupter. This is a purely mechanical device driven by a motor and
consists of two brass disks or wheels, Wa, Wb,, segments of which
are cut out of their peripheries, and these are filled with an insu-
lating compound or with segments of vulcanite, as shown in Fig.
118; the wheels are mounted on shafts, 8 8, and are insulated
FIG. 118. — ROTARY INTERRUPTOR.
from each other; two pairs of copper or carbon brushes, 1, 3, 2, 4,
are arranged to press firmly on the wheels like brushes on the
commutator of a dynamo. These brushes are in circuit with
the source of e. m. f. B, and the wheels are connected in
series through the primary Pt so that when the wheels and
brushes are in the position indicated in Fig. 114 a current will flow
through the inductor in the direction of the arrow, but upon the
movement of the wheels, which operate synchronously, through a
degree of arc equal to the peripheral length of a segment a re-
versal of the poles takes place and the current now flows through
the inductor in the opposite direction. In adjusting the brushes
care must be exercised that the pair marked 1 and 2 do not touch
the brass portion of their respective wheels simultaneously with
the brushes 3 and 4, but alternately these should rest on the in-
INTERRUPTORS.
121
sulated segments. When the rotary interrupter is in action, as the
first pair of brushes, 1, 2, forms contact, the current from the
positive pole flows through the disk Wa and the inductor P, thence
through the wheel Wb and the brush 1 to the battery. The next
instant the brushes 1 and 2 will occupy a position on the insulated
segment and 3 and 4 will form contact, when the positive current
will flow through the brush 3, traversing the wheel Wa and back to
mmmmm..v
AAAAAAT
FIG. 119. — DIAGRAM DISRUPTIVE DISCHARGE INTERRUPTOR.
the battery; by this means the current is reversed through the
inductor as many times per revolution as there are segments in the
wheels; and as these may represent a large number and the speed
at which the wheels are rotated may be very rapid, a large number
of alternations through the inductor per second may be obtained.
DISRUPTIVE DISCHARGE INTERRUPTOR. — A new type of inter-
rupter, based upon the principle of rendering an air gap conductive
by a disruptive discharge, is the invention of Thomas J. Murphy. In
the diagram Fig. 119, a direct or alternating current generator d, is
122 WIRELESS TELEGRAPHY.
connected by AAf to the terminals BC, forming a spark-plug ns; the
length of the gap is much greater than the potential developed
by a can break down. A small induction coil represented by DEF
having a condenser Q, shunted across the heads of the secondary,
connects to the principal air-gap, EC, through the spark-gaps H
HH1!!1. To prevent the current flowing continuously from
B to C for an indefinite period after the initial resistance of the
air has been disrupted by the sparks from the induction coil a mag-
netic blowout NS is mounted with its polar projections at right
angles to the carbons, thus forming the arc ; the magnetic field re-
acts on the arc, the disruptive discharge thereby interrupting the cur-
rent. When in action the generator a sends a current into the circuit
r
FIG. 120. — DISRUPTIVE DISCHARGE INTERRTJPTOR.
AAt which traverses the air-gap B C, along with the sparks from
the induction coil, and there will be as many interruptions of the
main current as there are sparks through the gap from the induo-
tion coil. This interrupter may be utilized for making and break-
ing currents having a potential of 500-volts; it operates most
efficiently on a 220-volt circuit. A very small induction coil may
be employed to primarily disrupt the air. A photograph, Fig. 120,
presents a general view of the Murphy interrupter.
EOTARY CONVERTER. — A modified form of the above type of
rotary pole changer has been placed on the market by the General
Electric Company of Berlin in connection with the Slaby-Arco
apparatus. It is known as the Grisson direct-alternating current
^Murphy High-Potential Interrupter. Collins. Elec. World and
Nov. 28, 1903.
INTERRUPTORS.
123
transformer,1 and, as its name implies, its purpose is to convert
a direct current into pure alternating currents in the inductor. Dif-
ferent from the ordinary type of interrupter, the Grisson converter
does not interrupt the current when the value of the latter reaches
its maximum, and this effectively eliminates the sparking at the
brushes B3 on the segmental wheels U1U- ; heavy currents may be
utilized for feeding the inductor in consequence, and the size of the
condenser may, therefore, be greatly diminished. In the diagram
Fio. 121. — DIAGRAM ROTARY CONVERTER.
Fig. 121, it is easy to follow the evolution of alternating currents
converted from the direct current ; the inductor pjp2p3 has, distinct
from its terminals P1P2, a third wire connected with a convolution
in the middle of the coil at P3. A direct current leads through to
the terminals L L1 ; the current leading in to L1 is divided at the
brushes 53 on the segmental disks ZJ1^2, which are attached to a
common shaft and insulated from each other, splitting the direct
current from the leads L L-, through the brushes Bz, forming con-
lScientific American, June 28, 1902.
124
WIRELESS TELEGRAPHY.
tact with the segments of the wheels, reversing the current as the
circuit is completed through the inductor. The direct current flows
to the inductor P1P2 for the period of time the brushes Bz are in
contact with one of the metal segments and one of the insulating
segments of their respective wheels when the circuit including the
inductor and the source of energy is closed, and the total voltage
flows through the inductor; but the instant this critical value is
reached the current is reversed in virtue of the change of position
of the conducting and insulating segments, and the current is
changed in direction in the inductor ; the iron core of the inductor
reverses its polarity with every alternation of current, and a counter
FIG. 122. — ROTARY CONVERTER.
e. m. f. is produced by means of cutting off the current
at P2P3 in the first circuit, and as one segment approaches and
the brushes begin to form contact the opposite segment leaves its
brush and the current is 'reduced to 0; when the first circuit is
thus broken the current in the second circuit quickly reaches its
maximum value. This converter has a frequency of from 400 to
6,000 alternations per minute, and while this is lower than, the
periods of electrolytic interrupters, heavier currents may be used.
The contact disks are revolved by means of a small motor, M,
operated by a shunt from the leads, LL1; C represents the com-
mutator and R a variable resistance for controlling the speed of the
disks U1U2, so that the converter has a comparatively wide range
of frequency. The Grisson converter is illustrated photographically
in Fig. 122.
INTERRUPTORS.
125
MERCURY VAPOR INTERRUPTOR. — The foregoing interrupters de-
scribed are designed to be placed in the primary circuit which
includes the inductor of the coil and source of e. m. f. A
FIG. 123.— DIAGRAM MERCURY VAPOR INTERRUPTOR.
FIG. 124. — MERCURY VAPOR INTERRUPTOR.
new interrupter invented by Peter Cooper Hewitt, is shown
in the diagram Fig. 123 and in half tone at Fig. 124,
126 WIRELESS TELEGRAPHY.
This interrupter differs from all other types in that it is placed
in the secondary circuit, and it not only interrupts the alternating
current of high potential, but serves as a modified form of spark-
gap. The mercury interruptor is constructed on the same general
principles as a mercury vapor lamp and consists of a glass globe
with inverted necks, from which the air is exhausted. The necks
contain a small quantity of mercury and make connection with
wires leading to the oscillator system. In action the negative
electrode offers an exceedingly high resistance to the high-potential
alternating current until a maximum critical potential difference is
reached, when it suddenly breaks down and the current flows
through the gaseous conductor with little or no opposition. When
the difference of potential between the positive and negative
electrodes drops to a minimum critical potential the resistance of the
positive electrode is instantly increased to its normally high value.
Eeferring to the diagram, 1 represents an alternating-current gen-
erator connected in series with the primary of a step-up trans-
former; 2' is the secondary winding of the transformer, the ter-
minals of which lead to the condensers 3, 3', with the interruptor
4, 4', 5 in shunt thereto. The condensers are connected with the
aerial wire, 6, and the earth, 7, but a closed circuit is obtained by
means of a variable inductance, 8. The rapidity of the interruptions
depends on the inductance of the coil, 8, and the capacity of the
condensers 3, 3'; the discharge from the condensers is oscillating
as in the case of the ordinary oscillator with a spark-gap, and the
voltage required to operate the interruptor varies from 2,000 to
20,000, the shape and size of the tube and coefficients of the circuit
determining the potential required.
CHAPTER XI.
OSCILLATING CURRENT GENERATORS.
PRACTICAL.
One of the fundamental requirements for the successful opera-
tion of long-distance wireless telegraphy is a high-frequency, high-
potential current. This may be produced by a number of different
methods, of which the induction coil, previously described, i« the
best known ; others are the f rictional machine, the Tesla oscillator,
the Thomson high-frequency apparatus, and the Fleming trans-
former. Experience has shown that enormously high fre-
quencies and potentials are not so desirable as they were at first
believed to be, but that oscillating currents having a periodicity of
100,000 per second and a potential of 25,000 to 50,000 volts give
the best results, since the former produces longer wave lengths,
which are more penetrating, and the latter backs up the current with
sufficient pressure to produce a heavy discharge, this giving
rise also to penetrating waves. The frictional machine and the
Tesla oscillator are not, therefore, in the present state of the art,
satisfactory generators, but the advances in the evolution of wire-
less telegraphy are so rapid that either of these devices may on the
morrow be found useful. A description of these methods is there-
fore appended.
FRICTIONAL MACHINE. — The frictional machine as invented by
Otto Guericke consisted of a globe of sulphur, axially mounted and
revolved by a crank; the generation of electricity was effected by
the friction of the hand against its surface. A glass globe was sub-
stituted by Bose, of Wittenburg, who also applied a smaller wheel
with a crank and belted it to the globe to increase its speed; the
electricity was collected on a metal tube. The plate glass machine,
shown in Fig. 125, was devised in 1787, and comprises a plate glass
disk, A, revolved on an axis by a crank having an insulated handle.
The friction is applied through the rubbers, D, pressing against the
disk of glass. The disk, rubbers and prime conductor are mounted
127
128 WIRELESS TELEGRAPHY.
on separate glass standards; the prime conductor, Pf consists of a
metal sphere carrying a metal comb extending on either side of the
disk.
The lower portion of the glass disk is covered with a silk bag to
prevent the leakage of electricity from the plate during its half
revolution from the rubbers to the collectors. The rubbers should
be coated with an amalgam made of 5 parts of zinc, 3 parts of tin,
and 9 parts of mercury melted together, pulverized, and made into
a paste with lard. Before the macli ine is used it should be dried in
a warm, place to expel all moisture.
In action, the plate glass machine is revolved toward the right,
when electricity is generated by the rubbers. When the charged
disk comes within the field of the collectors the electricity is accumu-
lated by the prime conductor, thus discharging the glass disk, which
Fio. 125. — FBICTIONAL MACHINE.
becomes negative, due to the loss of its charge. During each revolu-
tion of the plate every portion is alternately charged and discharged,
the lower half being constantly positive and the other half at zero
except its residual charge. The energy generated by a frictional
machine is proportional to the surface area of the plate-glass disk.
The length of the spark is not a true index of the energy generated,
since a short, thick spark may represent more energy than a long,
thin one. The greatest objection t< the frictional machine is its ex-
cessively high potential and proportionately low current strength ;
coupled with this untoward feature is the variation of spark due to
the humidity of the air and other atmospheric conditions. When
employed in wireless telegraphy a spark-gap should be provided by
mounting a metal sphere on a separate glass standard; the
aerial wire is connected to the prime conductor and the opposite
side of the spark-gap to the earth.
HoLT-ToPLER MACHINES. — In 1865 Holtz invented a machine
OSCILLATING CURRENT GENERATORS. 129
to generate electricity by its mutual static inductive influence. To
operate the machine it was necessary to give it an initial charge from
some external source. Topler improved upon the design by making
the machine self -exciting. In the Holtz type, Fig. 126, the plate A
is mounted axially on a shaft and revolves to the left by means of a
small driving wheel, to which a crank is attached. I,n front of the
revolving plate are the collectors V and H attached to the ebonite
disk M; the collectors K and L are insulated by the ebonite rods
extending from M ; these collectors are connected to the Leyden
jars, C, D, and with the adjustable spark-gap P, R.
The glass plate B is fixed on ebonite supports and remains sta-
FIG. 126.
tionary. Both the revolving and the stationary glass disks are
coated with shellac ; the stationary disk has two openings cut in it
immediately opposite the combs K, L; two inductors, T , X, made
of paper, are cemented on its rear surface. The Topler machine is
constructed on the same general principles as that of Holtz, but has
cemented on its front surface a number of tin-foil disks or carriers,
which form contact with wire brushes as the glass disk revolves;
two of these brushes are connected to the stationary plate and two
to the uninsulated collectors, thus making the machine self-exciting.
When in action and the plate A is revolved, the tin-foil carriers
come in contact with the brushes E, F, opposite brushes touching
each opposite pair of carriers successively at the same instant.
Electricity is generated by the friction produced and the carriers on
130 WIRELESS TELEGRAPHY.
A are charged as well as the inductors on B; the instant the carrier
is insulated from the inductor by the partial revolution of the plate
they act on each other inductively, and the process being continued,
the charge multiplies, finally charging the glass disk, which com-
municates its charges to the Leyden jars. When the potential
difference between the inner and outer coatings of the jars becomes
great enough through the cumulative action of the charged disks
the disruptive discharge takes place between the spark-balls and
oscillations surge through the circuit. For wireless telegraph
transmission the vertical wire is attached to one side of the spark-
gap and the earth terminal to the opposite side as in the case of an
induction coil.
FLEMING TRANSFORMER. — This method of producing- oscilla-
tions is described in connection with the DeForest system of
transmission, but is probably due to Dr. Fleming. It consists of an
alternating current generator connected in series with the primary
winding of an oil insulated transformer; the secondary terminals
are connected in series with a battery of Leyden jars or oil conden-
sers having a spark-gap in shunt thereto. When the condensers
are charged to their maximum capacity they discharge through the
spark-gap, converting the alternating high-potential currents into
oscillations of great intensity. This method bids fair to be univer-
sally adopted as a means of transformation for sending stations,
and possesses many desirable features over the induction coil;
among these may be cited that of utilizing any quantity of energy,
which in the induction coil is limited by the interrupter. The
great Marconi transmitters at Poldhu, Cornwall, England, Glace
Ba)', Nova Scotia, and South Welfleet, Mass., are equipped with
this type of apparatus.
TESLA OSCILLATOR. — In the Tesla oscillator a higher rate of
frequency and a higher potential are obtained than by an induction
coil or even a static machine. This result is accomplished by
stepping up the potential of an ordinary transformer by means of
a second transformer coil and stepping up the frequency of
oscillation by means of a second disruptive discharge. The Tesla
oscillator begins where the Fleming transformer leaves off, while it
differs from the Braun system of transformation in that it employs
a second spark-gap. A comparison of the diagrams A, B, C, Fig.
127, illustrates the physical difference in the apparatus of Fleming,
Braun ^nd Tesla.1
Martin, Inventions of Nikola . Tesla, 1894, p. 207.
OSCILLATING CURRENT GENERATORS. 131
Fleming's method is represented at A, Br aim's at B and Tesla's
at C. In Braun's method an ordinary induction coil,, 1, sparking
through the gap 2, is employed though an alternating-cur-
rent generator could be used to a better advantage; in either case
A
FIG. 127 B. — BRAUN OSCILLATOI
FIG. 127C.— TESLA OSCILLATOR.
the transformer, 3, steps up the potential of the current: the
terminals of the secondary lead to the antenna and earth and form
an open-circuit oscillator. In Tesla's oscillator after the ordinary
high potential is obtained by transformation through the coil, 1,
132
WIRELESS TELEGRAPHY.
and a frequency or ordinary periodicity is attained by means of the
spark-gap, 2, the oscillatory current is again stepped up by means of
the transformer, 3, when the potential may be further increased to
a million volts, and by discharging this high-potential current
across the spark-gap, 4, the frequency may be further stepped
up until it approximates 10,000,000 cycles per second, when
FIG. 128. — TESLA COIL.
the current assumes altogether new properties and produces phe-
nomena new and distinct from that of the induction coil or the
static machine, but it has not been proven of value in wireless
telegraphy to the present time.
The construction of a Tesla oscillator — that is, the second dis-
ruptive discharge-coil — is shown in the sectional drawing Fig. 128.
In a box, B, of hard wood encased in sheet zinc, the coil is placed.
This coil consists of two spools of hard rubber, R,R, held apart at a
distance of 10 cm. by bolts, c, and nuts, n, also of hard
rubber. Each spool comprises a tube, T, having an inside diam-
eter of 8 cm. and 3 mm. thick, the two flanges, F, F, 24
cm. square, being screwed thereon, leaving a space between
FF of about 3 cm. The secondary winding, s, sf of the
OSCILLATING CURRENT GENERATORS.
133
best rubber-covered wire, has 26 layers of 10 turns each. The two
halves of the secondary are wound oppositely and connected in
series, the connection between both being made over the primary.
The primary coil, P P, is wound in two parts and oppositely
upon the wooden spool, W , and the four terminals are led out of
FIG. 129. — ELIHU THOMSON MACHINE.
the oil through rubber tubes, t, t, having great dielectric strength.
Each half of the primary coil has four layers and 24 turns to the
layer; both of these parts are connected in series and the primary
and secondary layers are insulated by cotton cloth. The coil is held
in position in the oil on wooden supports and there should be at
least 5 cm. thickness of oil surrounding it. Either a com-
134 WIRELESS TELEGRAPHY.
mercial transformer, as that employed in the Fleming method, or
an ordinary induction coil having a spark-gap, may be employed
for the primary transformation as desired, although the former
gives the most uniform effects.
ELIHU THOMSON APPARATUS. — The photograph, Fig. 129, shows
the Thomson machine complete. The machine is composed of a
wooden casing, with glass sides and top, part of the ends, however,
being made to support the shaft projecting therefrom. There appears
to the right of the figure a pulley which is upon the shaft of a small
direct-current motor secured to the iron base, and occupying the
lower right-hand corner of the case. This motor also bears a pulley
with projections or studs carried on its face for engaging with the
perforated belt rising from it vertically, and passing over another
similar pulley on the connector frame of the shaft, which will be
alluded to later. The motor used is bi-polar, having slip rings and
taps to its winding for taking off single-phase alternating current.
It is, therefore, not only a motor, but an inverted rotary con-
verter, converting from continuous current to single-phase alter-
nating. The cycles are a little over 25 per second; this, of course,
depending on the speed of the motor itself, which in turn may be
regulated by the strength of the field of the motor. On the lower
left-hand portion of the case is a step-up transformer taking the low
voltage current from the motor or rotary converter and transforming
it to 15,000 to 20,000 volts in the secondary. This step-up trans-
former is specially made and insulated securely in the best manner
for these high potentials, solid asphalt being employed in insulation.
The secondary terminals are led upward within the case to the left,
and are connected to two arc-shaped pieces, insulated from each
other and arranged to come close to, but not to touch, two pins
on the revolving connector frame just below. To the right of these
arc-shaped pieces are a set of similar pieces arranged in two series,
corresponding to the two terminal pieces and having connections
led from them upwardly to the coils of a set of glass condensers.
The connections and arc-shaped pieces seen in front are those
which correspond to the positive foils, and those at the back
would correspond to the negative foils. On the assumption that the
arc-shaped piece connected to the secondary of the terminal, and
seen in front to the left, is a positive terminal, it is, of course,
anomalous to speak of positive and negative terminals in dealing
with alternating currents; but the significance of the use of this
term will be seen when it is understood that the revolving connector
OSCILLATING CURRENT GENERATORS. 135
frame bears connections and pins whereby the terminals of the high-
potential secondary are brought into contact with the condenser foils
so as to charge these foils to a potential of 15,000 to 20,000 volts
definitely as to polarity. This is accomplished by making the con-
nector frame in its rotation synchronous with the rotations of the
motor or rotary converter, and giving it a position to afford connec-
tion to the condensers when the alternating wave is at or near its
maximum in one direction only. When the opposite position is
reached, the frame is turned to a position such that no connection
can be afforded to the condensers.
The charging of the condenser plates or foils, as above alluded
to, takes place through a minute spark-gap between pins upon the
connector frame and the stationary arc-shaped pieces connected
with the foils. This avoids the noise of mechanical play or rubbing
and saves the wear which might otherwise take place. The con-
nector frame, therefore, revolves with entire freedom. It will thus
be seen that the connector frame in charging the condensers does
so with them in parallel or as one large condenser. The condensers,
however, on a semi-revolution of the frame arc connected one with
the other in series so as to add together the potential.
The same connection is made to the terminals, consisting of slide
rods and suitable supports on top of the machine, and bearing brass
balls and insulated handles. If there are ten condensers in a set, the
multiplying of the potential is, of course, ten times the charge
given to each condenser individually, which in the case of 15,000
volts would be 150,000.
As there are ordinarily about 25 revolutions per second, the dis-
charges of the condenser are at that rate, but of course are capable
of being varied over a wide range, both in number per second and in
intensity.
The machine is well adapted to wireless telegraphy, as it
does not reverse its polarity, the vigor of the discharges may be
regulated, and its operation is not dependent upon the weather;
besides, the machine is portable and can be used whenever a direct
current of sufficient voltage is at hand.
It may also be employed, as is evident, simply as a motor by
belting from the right-hand pulley and open-circuiting the primary
of the terminal. The terminal posts, as seen on the front board,
enable various connections to be made whereby the speed and voltage
can be controlled.1
better from Elihu Thomson to the author, May 20, 1903.
CHAPTER XII.
ELECTRIC WAVE ACTION.
HISTORICAL.
Prior to the time of Hertz's researches in 1888, the effects of
electric waves had been observed under varying conditions, but the
cause producing such phenomena was purely speculative. The
earliest reference to cohesion under electrical influence was made
by Guitard in 18501 who observed that when air laden with dust was
electrified from a point the particles of dust cohered into strings and
that the same phenomena occurs in the formation of snowflakes
under the action of atmospheric electrification and that small drops
of rain are cohered into large drops by the same process, the light-
ning thus giving rise to the thunder shower. In 1866 Mr. A. S.
Varley described his. observations on the opposition of a loose mass
of dust composed of conducting material to electric currents of mod-
erate tension. Varley made a large number of experiments with
lightning bridges based on the principle of a loose contact, but he
did not venture an explanation of such action.2 In 1879 Prof.
Hughes operated a wireless signaling apparatus at a distance of a
mile, using his microphonic carbon joint as a detector. Hughes sus-
pected the action to be due to electric waves, but could not prove
their existence. In 1884 Dr. Temistocle Calzecchi-Onesti made the
first device which has come to be called the coherer,3 and was the
first physicist to investigate the variability of conductivity of metal
filings under divers circumstances and conditions, and even carried
his researches to the point of connecting his tube with the prime
conductor of a frictional machine, and in this way obtained a lower-
ing of the resistance of the metal particles; but Calzecchi had no
knowledge of electric waves and ascribed the action of cohesion to
induction. In 1888 Hertz employed a metal ring for the detection
*Lodge, Electrician, London, Nov. 12, 1897. Elec. World and Eng., May
10, 1902.
2Varley's Paper, British Association (Liverpool meeting) , 1870.
*Nuovo Cimento. Reprinted in Elec. World and Eng., Dec. 2, 1899.
136
ELECTRIC WAVE ACTION. 137
of the electric waves,1 and in 1890 M. Eduard Branly read his
classical paper on "The Variations of Conductivity under Electrical
Influence/' being the first to show conclusively, by means of his
radio-conductor, that cohesion of metal filings was the effect of
impinging electric waves. He also made known the process of re-
storing the normally high resistance of the filings by percussion.
In 1894 Lodge read a paper before the Electrical Congress "On
the Possibility of Transmitting Signals with a Hertz Kadiator,"
employing a device modeled after Onesti's tube and Branly's radio-
conductor. In his researches on the phenomena relating to the action
of electric waves on metal filings Lodge found that the particles
were drawn into contact with each other or cohered, and so he gave
to the tube the name coherer, which, though not as euphonious as
the terminology of Branly, struck the key-note of popular sentiment,
and in its new form Lodge's name came to be inseparably linked
with it. Lodge was the first to apply the electro-mechanical tapper
as a means for automatically decohering the filings, an arrangement
which is in general use to-day in wireless telegraphy. Marconi
in 1897 improved the coherer to such an extent that in its present
form it is at once simple, sensitive, and fairly reliable, and is
typical of the evolutionary progress of scientific instruments.
An anomalous class of detectors which have been termed anti-
coherers, in virtue of their normal resistivity being enormously
increased instead of decreased, has been discovered by Herr Schaffer,
and still another form which is claimed to be electrolytic in action
by Herr Neugschwender. The fundamental principles involved
in the foregoing have been arranged in many different forms based
on the several theories to be described. Since the action of electric
waves is represented by the secondary effect of electric oscillations,
other methods of detection have been tried, with varying degrees of
success. Henry long ago observed the changes of magnetic polarity
in needles inserted in a coil of wire a distance of 30 feet from the
emitter.2 Elihu Thomson has also suggested the employment of a
device constructed on this principle8 of variation of magnetic per-
meability by the oscillating currents which are set up by the electric
waves. Kutherford was the first to actually employ this method
successfully, and Marconi has devised a detector based not only
upon magnetic permeability of a core of iron by electric oscillations,,
lSee Chapter III., Electric Waves.
'See Chapter V., Electric Oscillations.
^Proceedings Eng. Society, Western Penn. Kintner, 1901.
138 WIRELESS TELEGRAPHY.
but has rendered it much more sensitive and effectual by adding
a hysteresis effect. Fessenden has recently evolved a new electric
wave detector operated by the current of the oscillations instead
of by the voltage, as in foregoing devices, and his barretter,1 as he
terms his detector, is more sensitive than any yet devised for the
purpose.
THEORETICAL.
Branly offered several hypotheses to explain the probable me-
chanical effects produced by coherer action. He did not believe that
any displacement of the filings actually takes place on cohesion,
especially where the filings are held in position by extreme pressure,
or, again, as in the solid coherer mixtures. He thought it possible
that there might be a volatilization of the adjoining particles of the
filings and thus form a bridge of electrical conductivity. In the
mixtures of filings and non-conducting substances he offers the sug-
gestion that a change takes place in the dielectric itself and that
the insulating medium is broken down by the passage of minute
sparks and that the punctures thus made are coated with a conduct-
ing substance. Finally, Branly's theory attributes the coherer action
to the gradual breaking down of the dielectric of air insulating
the filings, the action being accelerated if the filings are compressed
and retarded if the pressure is diminished.
Lodge in studying the nature of metal filings under the in-
fluence of electric waves became convinced that the filings were
drawn together and cohered and that* the particles were welded
together, forming practically a continuous conductor. That the
primary cause of cohesion is due to a difference of potential set up
by the oscillating currents through the resonator circuit is well
established. Eccle in his investigations of this subject agrees with
Lodge in the matter of cohesion, but assumes that the critical po-
tential difference is established between the opposed plane surfaces
of the filings when the distance separating them is small as com-
pared to their own mass. According to Eccle, any particle of mat-
ter having the properties of conductivity, which is not spherical in
form, and which is free to move in the electric field established be-
.tween it and its fellows, has the property of exhibiting orientation
and thus of setting its longest axis parallel to the field. Accordingly
the process of cohesion by electric waves follows this order : ( 1 ) the
*U. S. Patent granted to Fessenden, Aug. 12, 1902.
ELECTRIC WAVE ACTION. 139
waves impinge on the resonator system, which (2) produces oscilla-
tions in this system, (3) causing a difference of potential between
the filings,, creating an electric field, and followed (4) by a purely
mechanical action or orientation, which results in (5) heat and
ends in (6) a welding process or cohesion.
Guthe, in his paper, "The Nature of Cohering Action/71 ex-
presses the opinion that the oscillations first heat the juncture of
the points of the metal filings where they form contact and that the
coherer effect follows. Shaw ascribes the orientation to a molecular
change in the metal particles and not to the filings regarded as a
mass.1 Guthe and Trowbridge conclude that the high original re-
sistance of the metal particles is due to the film of oxidization on the
surfaces of the filings. Bose's coherer theory supposes the electric
mass to act direct on the filings, and that the increase and decrease
of resistance under the action of electric waves is a phenomenon of
molecular strain and undergoes a physical and a chemical change
or modification of its properties in which cohesion is only one,
aspect.
Haerdon has observed the coherer effect with a microscope and
concludes that the action is electrolytic. His coherer consisted of one
contact only and was formed of two perfectly joined points. When
the incoming waves impinged on the resonator system he observed
that the sparks passed from one terminal to the other, carrying
minute particles of matter, when a bridge was formed connecting
the two points and possessing the property of conductivity until
broken down by the usual method of percussion or tapping process.?
In the current operated wave detector of Fessenden, a low heat
capacity of the platinum wire must be maintained, so that the con-
ditions are such that the radiating surface is reduced to a minimum ;
this is the reverse of the action of the bolometer, which has a large
heat absorbing and radiating surface compared to its mass ; for this
reason Fessenden employs a cylindrical wire, since its surface per
volume is smallest. The theory of the action of the hot-wire de-
tector involves a new discovery, namely, that "if a conductor having
a specific heat-factor of such value that the latent energy required to
heat it to a certain excess above the air is small relative to the energy
lost by radiation, convection and conduction at that excess tempera-
ture during the time of a signal, then it is possible to so arrange the
conducting wire in a local continuous current circuit so that when a
Philosophical Mag.
2Annalen der Physik.
140 WIRELESS TELEGRAPHY.
given amount of current of any periodicity or wave form is caused
to flow through the conducting wire there will be a corresponding
change of the same magnitude in the local circuit."1
EXPERIMENTAL.
The exceedingly high resistance of metal filings had been ob-
served long before Branly gave his attention to the subject, as well
as the decrease in resistance when pressure is applied; by varying
the pressure from zero to infinity the resistance may be made to
drop from many megohms to practically that of a solid metal con-
ductor. But not only has pressure the property of decreasing
the resistance of metal filings, but electric waves will work a change
in the metal filings of a coherer so that from a non-conductor
it will become a very good conductor of electric currents. In
order to test the action of electric wave&
it is necessary that the coherer should
be placed in series with a galvanometer
or telephone receiver and a single cell
of chloride of silver or other source of
FIG. 130. e- m. f., as in Fig. 130.
INTERNAL COHERER CIRCUIT. This Constitutes a circuit for the pas-
sage of the direct current of the cell which is to register the drop
in resistance of the coherer, as well as a closed-circuit resonator for
the surging of the electric oscillations set up in it by the impinging
electric waves. Now if a Leyden jar is discharged a few meters
away, there will be instantly a deflection of the galvanometer needle
or a click in the telephone. Repeating the spark increases the con-
ductivity of the coherer, and successive sparks sending out trains
of waves will break down the resistance finally, which a single spark
emitting a train of waves will be unable to do. This is an exceed-
ingly important factor in syntonic wireless telegraphy, and is one
of the fundamental principles underlying it.
When a coherer is adjusted to a certain critical sensitiveness, the
filings may cohere immediately before the spark passes between the
oscillator balls. This may result from two causes, (a) from a train
of waves emitted by the mechanical interrupter, or (b) from the
low-frequency, high-potential alternations set up in the oscillator
»U. S. Patent Fessenden. Aug. 12, 1902.
Q j|
ELECTRIC WAVE ACTION. 141
system of the coil and producing a strong electrostatic field. Cal-
zecchi and Branly both found that pulsating and direct currents
of high e. m. f. produce cohesion; in the light of recent knowledge
it seems that in either case the conductivity of the coherer is in-
creased by the potential difference between the irregularly shaped
particles, and this follows the same law as cohesion under the action
of electric oscillations. Branly tested the drop in resistance of the
following metals1 during the action of electric waves : iron, copper,
brass, zinc, antimony, aluminum, tellurium, cadmium, bismuth, and
lead, and determined that the property of cohesion depended largely
on pressure and that very fine metal filings after percussion offered
an almost perfect barrier to the passage of a feeble direct current ;
the proper value to insure a maximum sensitiveness may be easily
obtained by means of adjustments of the terminal conductor plugs of
the coherer. Branly noted that a layer of copper reduced by hydrogen
and spread on a sheet of roughened ebonite 2 cm. wide and 7 cm.
long and well polished has quite a range of variability. Other
substances were also experimented with, including galena, pow-
dered bioxide of manganese mixed with antimony and com-
pressed. Platinized and silvered glass and glass covered with gold,
silver and aluminum foil were also susceptible to cohesion, and
when iron filings were mixed with colza oil or petroleum they were
likewise affected ; even solids consisting of iron filings and Canada
balsam were reduced in resistance from thousands of ohms to a few
hundreds by the disruptive discharge. Rods of solid fused flowers
of sulphur and aluminum filings and of solid copper bars oxidized
and laid across each other also showed a marvelous decrease in re-
sistivity when the spark passed. The normal resistivity may be
restored by percussion, and to accomplish this Branly employed a
mechanical tapper, the hammer of which could be regulated. Some
substances would retain an increase of conductivity for a period of
24 hours, and in others the normal resistivity would be instantly re-
stored; coherers of this order are designated auto-coherers, self-
righting or self-restoring coherers, as fancy dictates. Other sub-
stances could be restored to normal resistance by heating. Branly
also observed substances in which there was an increase of resistivity
under the action of electric waves ; antimony and aluminum filings
exhibit a marked increase in resistance; these detectors are called
anti-coherers, and a kind of platinized glass employed as a coherer
lComptes Rendes, Vol. III., 785, and vol. 112, p. 90.
U2 WIRELESS TELEGRAPHY.
would increase and diminish in resistance alternately. KoepsePs
researches led him to the conclusion that the harder the metal filings
the greater the accuracy in decohering, and therefore recommends
highly tempered steel filings. Guthe ascertained that the potential
difference increases with the strength of the current until it reaches
a certain constant value, when any further increase has no effect
on it; this he calls its critical value. Tommasina has made some
beautiful experiments in cohesion by electric waves. His apparatus
consisted of a nickel-plated brass ball a centimeter in diameter., sus-
pended by a thin wire; a few mm. from the ball and immediately
under it a copper disk 15 mm. in diameter was delicately poised
on a copper spring. Connected in series with the ball and disk
was a battery. Some nickel filings were now placed on the disk,
the ball lowered to a point of slightest contact and the current
switched through the circuit, when on gently elevating the ball the
filings were found to cohere in series, forming a little chain nearly
a centimeter in length; with carbon granules, chains 15 mm. in
length were obtained.
There are other substances than those tested by Branly which
possess the property of responding to electric waves, and among
them may be mentioned a preparation of frog's-leg nerve and
muscle, as shown by Kitter,1 and the author has succeeded in show-
ing the "coherer effect" of electric waves acting on the human
brain.2 These experiments are interesting only from a physiological
standpoint. The detection of electric waves by a comparatively
new and entirely different process from that of cohesion is the class
of detectors based on magnetic permeability. Great results are ex-
pected of magnetic detectors by many authorities, for it is reasoned
from theoretical considerations that all the energy of the impinging
wave may be utilized against the amount merely required to raise
the potential to certain value where the insulating films break down
and waste the rest of the wave, as in the case of the coherer. The
great advantage of this detector is in its self-restoring qualities as
well as that its resistance is practically the same at any moment,
whereas in a coherer before and after tapping there is always a wide
diverging in its resistance, and this effects a considerable variation
in the workings of the recorder. It is also claimed that it is more
lrThe Works of Hertz and Some of His Successors. Lodge.
"Effect of Electric Waves on Human Brains. Collins. Elec. World
and Eng. Feb. 22, 1901.
ELECTRIC WAVE ACTION. 143
sensitive and much more uniform in action than the coherer, and
will, therefore, be of great value in syntonic wireless telegraphy.
While this is undoubtedly true, its lack of variability between
resistivity and conductivity is decidedly disadvantageous, since a
relay, however delicate, cannot be operated with it, and its usefulness
is therefore limited to the telephone as an indicator, and in this it
acts similarly to a carbon coherer, which is likewise self-restoring,
i.e., returns to its normal resistance without tapping.
Dr. Lee DeForest and Mr. E. H. Smythe made an extended
investigation into the cause and effect of substances in which the
electric oscillations proved a resistance in the detecting medium1
instead of decreasing it, as in the filings coherer; this responder is
not, however, an anti-coherer in a strict sense, but is based upon the
disruptive action of high-frequency currents. When two electrodes
are. slightly separated, and a mixture of oxide of lead and glycerine
or other suitable medium is interposed between their opposed sur-
faces, and are then connected in series with a source of current,
minute metallic particles are detached from the anode and thence
carried across the gap separating the electrodes to the cathode,
where they build up bridges which extend toward and soon reach the
anode, bridging the gap, and thus lowering the resistance of the
local circuit, as shown in Fig. 131a. These metallic threads de-
posited by electrolysis are pro-
duced by the local current. When
the oscillating current is set up
by the impinging waves, it breaks
FIG. 131 a. down the metallic threads, giving
— ELECTROLYSIS BY DIRECT CURRENT. > 51Y1"5
it the appearance indicated in Fig.
131&, segregating and precipitat-
ing the metallic particles quite
-— • i- •%% gently, instead of violently dis-
FIG 1316- rupting them, though the action
DISRUPTION BY OSCILLATING CURRENTS. is practically instantaneous.
TESTING THE COHERER. — Kins-
ley suggests the following way for testing a coherer by what he terms
the potential difference method. He assumes that all metals are
equally sensitive and that any degree of sensitiveness may be
obtained by applying the requisite pressure to the filings by means
of the coherer conductor plugs. When the resistance of the filings
. World and Eng., April 11, 1903, p. C13.
144 WIRELESS TELEGRAPHY.
is infinitely great, they do not decrease in resistivity* gradually, but
remain practically constant until the potential difference assumes
a critical value, and the resistance then drops, just as in the case
of a disruptive discharge between oscillator balls. According to
Kinsley, metals oxidizing readily must be much more carefully
treated in the construction of coherers than those which do not
oxidize so easily. Nickel gives the best results, for the reason that
it can be manipulated in the open air and gives a high resistance —
and therefore sensitiveness — as required in wireless telegraphy. The
voltage for operating a relay through a coherer should not be greater
than 0.4 and the current only 0.002 to 0.001 ampere.
The adjustment of a coherer is accomplished by placing it in
series with a cell giving the current and voltage just cited and the
relay wound to the resistance it is intended to use. The coherer
conductor plugs should be withdrawn so that it has a resistance of
several megohms. The armature of the relay should have a play of
one-tenth mm. and just clearing the poles of the magnets. The
tension of the spring should be very slight — merely sufficient
to draw the armature away from the magnets when there is no
current flowing through the relay coils. The current is now passed
through the circuit, the conductor plugs being manipulated to a
nicety until the turn of a one-tenth mm. of the adjuster screw of
the relay armature causes the latter to be drawn to or from the
poles; when drawn from the poles by the adjustment of the con-
ductor plugs the coherer may be said to be roughly correct. Tap the
coherer with a pencil while testing to prevent premature cohesion,
which is apt to occur either from pressure or from the potential
caused by the local battery circuit. Test finally with the spark
from a Leyden jar or oscillator system of a coil.
Another method for testing the sensitiveness of a coherer is to
place it in a series with a telephone receiver and a source of current
having a small e. m. f . By adjusting the coherer plugs while listen-
ing to the receiver the characteristic sounds will easily enable the
operator to determine when the critical value has been reached ; and
when the maximum sensitiveness of the coherer is reached the flow
of the current is continuously heard. The plugs should now be
sealed in the tube, In actual practice coherers may be tested by one
of the above methods and then further tested at a distance of 20 or
30 kilometers.
CHAPTER XIII.
ELECTRIC WAVE DETECTORS.
PRACTICAL.
Electric wave detectors were invented before electric waves were
known to exist. There are two classes of detectors, i.e., voltage-
operated detectors and current-operated detectors. These classes
may be subdivided into several distinctive types, the principal ones
being the coherer, auto-coherer, hot wire barretter and electrolytic
responder. These various detectors will be described in the rota-
tion in which they were made public.
CALZECCHI TUBE. — Calzecchi-Onesti devised a coherer consist-
ing of a tube filled with metal filings to which there was attached
FIG. 132.— CALZECCHI TUBE.
a small crank, Fig. 132, and by turning the crank half a revolution
the filings were caused to decohere.1
HERTZ RESONATOR. — This consisted of a ring with a microm-
eter spark-gap, as shown in Fig. 20 ; it has been mentioned through-
out this work and will not need further description here. With the
wire detectors of Hertz no local batteries were used or additional
apparatus to increase or magnify the effects of the waves.
BRANLY RADIO-CONDUCTOR. — Branly's radio-conductor, shown
in cross-section, Fig. 133, is an ebonite tube, 1, having one of its
lNeuvo Cimento, 1884.
145
146
WIRELESS TELEGRAPHY.
conductor plugs, 2, arranged like a piston so that a maximum or
minimum pressure may be applied to the filings in the cavity, 3;
FIG. 133. — BRANLY RADIO-CONDUCTOR.
to complete the circuit the opposite terminal conductor plug, 4, is
used ; the terminals, 5, 6, in contact with the filings may be employed
instead of 2 and 4, by which Branly showed the decrease of re-
Fio. 134. — OXIDIZED RADIO-CONDUCTOR.
sistance was equal in every direction. A simpler form of radio-
conductor was devised by Branly, and is shown in Fig. 134; the
arrangement consisted merely of two oxidized copper bars laid at
ELECTRIC WAVE DETECTORS.
147
right angles one upon the other. The author increased the sensitive-
ness of this arrangement by having the upper rod ground to a knife
edge and allowing this to rest lightly on the lower rod.
LODGE COHERER. — Lodge's coherer was an improvement on those
FIG. 136a. —
SINGLE CONTACT COHERER.
FIG. 135. — LODGE COHERER.
of Calzecchi and Branly in that the tube was mounted with the
conductor plugs having a screw adjustment so that the pressure on
the filings might be varied between
wide limits. Fig. 135 represents the
Lodge coherer, half size, that is to say,
the original was 12 cm. in length and
had a bore of about 8 mm. Two other
forms of coherers designed by Lodge
are shown in Figs. 136 and 137. In
Fig. 136 a turn of thin iron wire, B, is mounted on an adjustable
lever — shown at A — and impinges on a small piece of aluminum
connected with one of the binding posts and the adjustable wire
with the opposite post. The second
form is shown in Fig. 137. It also
depends on an imperfect electrical con-
tact, and is therefore essentially a co-
herer. A metal point rests lightly on
a metal diaphragm and under the ac-
tion of the waves the point coheres to
the disk, and is made to decohere by
means of a small rack.
OTHER WAVE DETECTORS. — A type
of detector based upon the principle that gas possesses greater
conductivity when disturbed by electric waves than in its nor-
mal state has given rise to the vacuum and trigger tubes
for experimental observation. Zehnder's trigger tube, shown
half size in Fig. 138, gives better results than an ordinary
vacuum tube ; the terminals, A, B, are attached to the resonator
plates, and C and D to a high-potential current which is on the
FIG. 1366.—
SINGLE CONTACT COHERER.
148
WIRELESS TELEGRAPHY.
verge of breaking down the resistance of the tube and causing it to
glow; the impinging electric waves supply the additional potential
in the form of oscillatory currents and the tube becomes luminous.
1+
^*K
fl
FIG. 137. — POINT AND DIAPHRAGM COHERER.
Fitzgerald employed a sensitive galvanometer as a detector, the field
of force created by the oscillations exerted a final influence through
FIG. 138.— ZEHNDER TRIGGER TUBE DETECTOR.
the galvanometer system. The ther-
mopile, the thermal joint, the bolo-
meter, and the action of electric
waves on wires have been used as
detectors by Paalzow and Arons, Eu-
bens and Eitter. Gregory employed
a sensitive expansion meter con-
structed on the principle of a Car-
dew voltmeter. Bjerknes employed
a rectangular form of the Hertz
resonator (Fig. 139) tuned to the
oscillator, and instead of a spark-gap, one side of an electrometer
was connected in;1 the needle was at 0 potential, and therefore at-
tracted by both quadrants; with this detector Bjerknes plotted
'Signalling Through Space Without Wires. — Lodge.
FIG. 139.—
BJERKNES QUADRANT DETECTOR.
ELECTRIC WAVE DETECTORS.
149
curves showing the persistency and damping influence of open and
closed resonator systems.
Boltzman used a micrometer air-
gap connected to an electroscope, as
shown in Fig. 140. A current of
considerable potential is prevented
from discharging across the spark-
gap of the electrometer until the thin
insulating film of air becomes ionized
by the electric waves and allows the
current to pass, thus deflecting the
leaves of the electroscope. As Lodge
has pointed out, with this simple ap-
paratus electric waves could have
been easily discovered a hundred
years ago. A detector used by
Eighi depended for its resistivity on a film of finely divided
mercury on a piece of glass and evidently worked on the
principle of the air-gap. Popoff, in his meteorological ex-
periments, made a coherer by pasting two strips of platinum foil
FIG. 140.—
BOLTZMAN AIR-GAP DETECTOR.
FIG. 141. — MARCONI COHERER.
on the inside of a glass tube; the ends of the strips of foil were
brought outside the tube ; the filings were placed on the gap between
the pieces of foil and filled the tube about half full.
MARCONI COHERER. — Marconi's coherer is an improvement on
Lodge's modification of Branly's radio-conductor; he ascertained
150
WIRELESS TELEGRAPHY.
and employed the most sensitive and accurate combinations and
quantities of metal filings — 90 per cent, nickel and 10 per cent,
silver — enclosed in a space of 1 square mm. cross-section. His
coherer is shown in full size in Fig. 141. With it he has been able
to detect signals a distance of 1,099 miles. The terminal conductor
plugs are of silver with platinum leads sealed in an exhausted
glass tube. The object of creating a partial vacuum in the tube
is to prevent the filings from succumbing to oxidization. The con-
ductor plugs are sometimes amalgamated with mercury, but too
great a percentage of mercury is fatal to the proper working of the
coherer. It is not necessary to exhaust the tube to insure a working
coherer within certain limits. A simple coherer for laboratory
work is shown in Fig. 143. Two brass conductor plugs, a, a^
FIG. 143. — EXPERIMENTAL COHERER.
slide freely through the brass standards, b, &/ mounted on a piece
of hard rubber, c; the terminals of the plugs, a, a', are of silver
or brass 1 mm. in diameter and sliding nicely in a piece of glass
tubing. The plugs a and a1 are fitted with a screw adjustment to
obtain an inward pressure, the springs d and d1 drawing the plugs
apart when a higher resistance of the filings is desired. The set-
screws, e, e1J are provided to secure the plugs when the proper ad-
justment is obtained. The filings should occupy a space 1 mm. in
length and the bore of the glass tube should be about 1 mm. in
diameter.
SLABY-ARCO COHERER. — The coherer used in the Slaby-Arco in-
struments consists of silver conductor plugs with platinum termi-
nals, and the coherer is exhausted for the reasons stated above, a*
ELECTRIC WAVE DETECTORS. 151
well as to keep the filings at all times perfectly dry and movable.,
thus permitting the original grouping of the filings after each per-
cussion. The end surfaces of the conductor plugs are not parallel
but wedge-shaped, as in Fig. 144; this "split" or pocket of the
coherer allows its sensitiveness to be regulated after the tube is
exhausted and sealed. If the position of the tube is such that the
narrow part of the split is down, the filings assume a vertical posi-
Fio. 144. — SLABY-ARCO COHERER.
tion, the pressure is increased by gravity, and its sensitiveness is at
its maximum value. If the broad part of the "split" is down the
filings are spread lengthwise, the pressure is diminished, and its
sensitiveness decreased. A very sensitive coherer is seldom accurate
enough for commercial work, but by this arrangement the proper
relations of sensitiveness and accuracy are easily arrived at. The
different positions of the coherer are obtained by means of an
adjusting pinion and a catch spring. Metal caps are attached to
either end of the coherer tube, making the exchange of coherers very
easy.
BRAUN COHERER. — The Braun-Siemens and Halske coherer is
constructed on original lines. Its essential feature is that it does
away with exhausting the tube. Braun contends that experiment
had not shown the vacuum tube to be more sensitive than are the
unexhausted ones. It is true that the vacuum coherer is exceedingly
difficult to keep in adjustment, even transportation sometimes de-
ranging it and when its sensitiveness is lost it is practically worth-
less. Braun's coherer may be restored to its initial state of sensi-
tiveness with ease; it may be taken apart, cleaned, reconstructed,
and adjusted by any practical operator. The conductor plugs are
of steel and the filings are of hardened steel after Koepsel's formula.
The ends of the conductor plugs forming contact must be highly
polished. In sensitiveness it is practically equal to the best vacuum
nickel-silver filings coherer and its accuracy greater, that is to say,
it is not as susceptible to atmospheric disturbances. Its different
parts are shown in Fig. 145.
Braun made the observation that the steel filings coherer does
not respond as quickly and is not as accurate when the conductor
152
WIRELESS TELEGRAPHY.
plugs become magnetic, but that a certain critical magnetism in-
creases its sensitiveness without decreasing its accuracy. He, there-
fore, devised a magnetic regulator consisting of a permanent ring
magnet and placed near the terminal surfaces of the conductor
plugs. By rotating the ring magnet the opposite poles may be
brought near the ends of the plugs and the plugs magnetized or de-
FIG. 145. — BRATJN-SIEMENS AND HALSKE COHERER.
magnetized to any extent desired. Nearly all systems of wireless
telegraphy employ the regulation coherer, which requires tapping to
restore it to its normal state of resistivity, but another sub-class of
coherers are made which return to the normal resistance without
FIG. 146. — BLONDEL REGENERABLE COHERER.
tapping ; these are termed self-righting, self-restoring, auto-coherers,
or microphone coherers. They are far more sensitive than those
requiring percussion, but this is due to the exceedingly high re-
sistance which is a condition required in self-righting coherers. By
ELECTRIC WAVE DETECTORS.
153
increasing the pressure on the filings or granules any self-righting
coherer may be transformed into a percussion coherer. Carbon
granules are usually employed in self -restoring coherers.
BLONDEL REGENERABLE COHERER. — Blondel's regenerable co-
herer. Fig. 146, was designed so that the filings in the coherer
pocket could be changed, fliminiphed or increased, after the air was
exhausted from the tube. The coherer proper is similar to the
ordinary type, but has the additional U-shaped
tube blown immediately over the pocket and at
right angles to it. The inverted U-tube, which
is much longer at its free end than the arm con-
nected with the pocket, contains an additional
supply of metal filings, and by turning the U-
tube and the coherer round the axis of the lat-
ter, the quantity of filings in the pocket may be
varied. Guarini has adopted this form in his
repeater system of wireless telegraphy. The
Ducretet coherer is similar to the Blondel, but
the pocket is V-shaped and the filings are of
hardened steel. It is shown in Fig. 147.
SCHAFFER ANTI-COHERER. — The Schaffer system is character-
FIG. 148. — BRANLY TRIPOD COHERER.
ized by its use of an anti-coherer. It is made on the principle of the
Righi coherer, but is formed of a silver deposit on glass, which is
154
WMELEtiti TELEGRAPHY.
divided by a minute air-gap made with a razor edge; it is then
covered with a film of celluloid.
BRANLY TRIPOD COHERER. — The two most recent coherers are
the Branly tripod and the Castelli or Italian Navy self-restoring
tube. The new Branly coherer consists of two disks of metal, in one
of which are fixed three metal rods forming a little tripod. The
points of these rods are rounded and slightly oxidized. These rest
on the second disk, which is of polished steel. The degrees of oxidi-
zation of the metal points and the polish on the steel disk are an
essential factor in the resulting sensitiveness. The thin film of
oxide will remain unchanged for several months. Branly devised
this form to eliminate the multiplicity of contacts as in the ordi-
nary coherer and which is the principal cause of its uneven vari-
ability. Fig. 148 shows its form.
CASTELLI COHERER. — The Castelli coherer is said to have been
employed by Marconi in his recent transatlantic cableless tests, and
A c consists of a tube, A, Fig. 149, with
^^)yW//j!// conductor plugs, B, B, formed of
ft ^\* carbon, a central core of iron, C,
FIG. i49.-CAs^LLi AUTO-COHERER, leaving the dual pockets, D, D, to
receive two drops of mercury. The
tube is self-decohering and in practice it insures regularity and
rapidity equal to the best auto-coherers.
FIG. 150a. — FESSENDEN MAGNETIC
DETECTOR. (Side Elevation.)
FIG. 1506. — FESSENDEN MAGNETIC
DETECTOR. (Top Elevation.)
FESSENDEN MAGNETIC DETECTOR. — Fessenden employed in his
earlier experiments a magnetic wave detector,1 shown diagrammat-
ically in Fig. 150, a, 1. 1 is a small silver ring, with a mirror.
^Proceedings Eng. Society Wester^ Penn. Kintner, March 19, 1901.
ELECTRIC WAVE DETECTORS.
155
2, attached to it, and the system suspended by a quartz fibre ; 3, 3'
are two coils of wire connected in series, the free terminals, 4 and 5,
of which are connected to the vertical wire and the earth. High-
frequency oscillations are set up in the coil by the impinging elec-
tric waves, the oscillations in the coils producing a magnetic field
between them; as these lines cut through the silver ring, currents
are induced in it having a tendency to set the ring at right angles
to the surface of the coils; this is caused by the field so created
tending to equalize the magnetic opposing forces. The slightest
movement of the ring and mirror is easily detected and determined
by means of a reading telescope and scale. A condenser of proper
capacity in parallel with the windings of the coils will increase its
action.
That a telephone receiver may be employed instead of the mir-
ror and scale just described, to read the signals, the arrangement
shown in Fig. 151 was devised;
a metal ring, 1, rests lightly on
three knife edges, 2, 2', 3 ; two
of these knife edges, 2, 2', are
of metal fastened inside the
larger ring, and the third knife
edge, 3, is of carbon. An alter-
nating current from a dynamo,
(>, passes through a non-induct-
ive resistance; from this a lead
runs to the knife edges, 2, 2',
and an opposite lead connects
with the carbon knife edge, 3,
through the telephone receiver, 5. This forms a shunt from the
dynamo circuit. The vertical wire is attached to the large ring,
and from the carbon knife edge a terminal leads to earth.
MARCONI'S MAGNETIC DETECTOR.1 — As in those above, this de-
tector depends upon the varying magnetic lines of force produced by
high-frequency oscillations set up in the detector by waves emitted
from a distant point ; but there is another factor equally important
in this detector, and that is hysteresis, or theH B curve which takes
place when a piece of iron is magnetized and demagnetized. Since
the ascending and descending curves do not coincide, some work
must be done; this takes place in the form of heat, and this magni-
1 Journal of the Society of Arts, London. Marconi, 1902.
Fio. 151.—
3ENDEN DETECTOR. (Second Form.)
156
WIRELESS TELEGRAPHY.
fies the effects of the oscillations. In construction the magnetic
detector is simple; a layer of fine insulated copper wire, Fig. 152,
is wound on a core made of thin iron wires. A second layer of fine
insulated wire, 2, is wound on the first, forming a secondary coil.
The ends of the inner or primary coil are connected with the an-
tenna and ground.
The terminals of the secondary coil are connected in series with
a telephone receiver or other suitable receiving device. In Mar-
coni's magnetic detector a horseshoe magnet is caused to revolve
before the poles of the iron core by clockwork, and a constant
M
A
FIG. 152.— MARCONI MAGNETIC DETECTOR. (First Form.)
change occasioned by successive reversals of magnetism is produced.
The magnet should be revolved very slowly, half a revolution per
second, the speed being changed for different qualities of iron em-
ployed. The great advantage of the magnetic detector lies not
only in its self-restoring properties, but in its resistance remaining
constant during the passage of the oscillation as well as in the in-
termission. In this respect it will prove extremely advantageous
in syntonic wireless telegraphy. Its disadvantage lies in its limited
range of usefulness, since the wide divergence between resistivity
ELECTRIC WAVE DETECTORS.
157
and conductivity necessary in a detector to operate a relay is in the
magnetic detector lacking, and accordingly a telephone receiver or
other sensitive device must be employed in connection with it.
DEFOREST ELECTROLYTIC RESPONDER. — In the DeForest elec-
trolytic anti-coherer the terminal conductor plugs or elec-
FIG. 153. — DEFOREST ELECTROLYTIC RESPONDER.
trodes employed, Fig. 153, arc about an eighth of an inch in
diameter and separated one-sixteenth of an inch ; the oppositely
FIG. 154.— LODGE MERC
disposed surfaces may be either smooth or roughened. A screw
adjustment is provided for accurately adjusting the sensitiveness of
the responder. The complete detector consists of an insulating tube
158
WIRELESS TELEGRAPHY.
of glass or ebonite. In the interspace is the sensitive medium com-
posed of rather coarse filings and oxide of lead in equal bulk and
made into a paste by the addition of glycerine or vaseline with a
trace of water or alcohol. The local current should have a small
value — one-tenth to one milliampere — and a variable resistance,
ranging from 0 to 15,000 ohms, is included in the circuit to obtain
the proper relation of current to resistance.
LODGE MERCURIAL COHERER. — A new form of mercurial co-
herer brought out by Lodge is shown in Fig. 154 photographically,
and in Figs. 155, a, &, in cross-section and plan and possesses sev-
eral new features. It is sensitive enough for wave detection at long
distances, having a variability ranging from maximum resistivity
to maximum conductivity equal to the best filings coherer and
FIG. 155a.—
CROSS-SECTION LODGE COHERER.
Plan
FIG. 1556.—
PLAN OF LODGE COHERER.
without the disturbing element of mechanical decohesion of
the latter. The Lodge coherer is devised so that fresh and uni-
formly exposed surfaces are constantly in action for the process
of cohesion. This is accomplished by causing a small steel disk
to revolve continuously in contact with a column of mercury,
between which is interposed a thin film of oil. When in action,
the instant cohesion is effected between the molecules of the solid
and fluid metals disruption is produced by the partial revolution
of the disk when freshly. exposed surfaces are brought into position
ready for the next impulse. In Figs. 155 the rotary wheel is indicated
by a; an amalgamated platinum wire spiral, b; c is the. connection
between the wire & and the binding post, h; dd is a trough of mer-
ELECTRIC WAVE DETECTORS.
159
cury, the copper brush, e, making contact with the axle, /, to which
the disk is fastened; a spring, /, having a small piece of felt, k,
attached rests lightly on the disk, keeping its surface clean and
dry. The disk is revolved by gears of ebonite operated by clockwork
which also actuates a syphon recorder. The coherer is connected
directly in circuit with the syphon recorder; without the inter ven-
Fio. 156. — MARCONI COMMERCIAL MAGNETIC DETECTOR.
tion of a relay or other device, the local current should be kept from
0.03 to 0.5 volts ; when the potential difference exceeds this the film
of oil will be broken down and the recorder set in motion.
MARCONI MAGNETIC DETECTOR (SECOND FORM). — This is the
commercial form of magnetic detector now employed by Marconi.
It consists of a small glass tube, AA, on which is wound a primary
made of a single layer of wire, BB, the terminals leading to the
aerial and earth wires respectively, as shown in Fig. 156. A second
coil of wire, 0, is slipped over the primary and the terminals of
this connect with a telephone receiver, D; two grooved wheels, 4
inches in diameter, are connected by a flexible band formed of a
number of thin iron wires, FF, which is made to travel through the
glass tube by means of a spring motor enclosed in a case.
Two steel horseshoe magnets, GG, are placed closely to the mov-
ing band of wire and adjusted until the maximum effect is obtained.
When oscillations are set up in the resonator which includes the
primary coil, BB, they change the magnetic intensity of the moving
band of iron wire and thus currents are set up in the coil, C, and
160
WIRELESS TELEGRAPHY.
the telephone receiver, D. The magnetic detector is shown photo-
graphically in Fig. 157.
FESSENDEN HOT-WIRE BARRETTER. — A current-operated wave
FIG. 157. — MARCONI MAGNETIC DETECTOR.
detector1 that is more rapid and sensitive than a filings coherer, and
one which does not require tapping, is the
invention of Fessenden. It is shown in
detail in Fig. 158, and consists of a short
loop of silver wire, 1, having a diameter of
.002 and having a platinum core .00006 of
an inch in diameter, the terminals being
fastened to the leading-in wires, 6, 6, which
are sealed in the glass tube, 3. The tip of
the loop is immersed in nitric acid and the
silver is dissolved away, leaving a minute
platinum surface exposed; this is done in
order that the conductor losses will exceed
the radiation losses, and to further decrease
the loss of radiation by heat the loop is en-
closed in a silver shell, 5, 5 ; the bulb is then
exhausted to further increase the effectiveness of the detector.
FIG. 158 —FESSENDEN HOT-
WIRE BARRETTER.
»U. S. Patent. Fessenden, N. 706,744, Aug. 12, 1902.
ELECTRIC WAVE DETECTORS.
161
FESSENDEX LIQUID BARRETTER. — A liquid barretter
or current-actuated de-
tector may be constructed
in different forms,1 the
simplest being shown in
Fig. 159a; in this case
the loop of a metal bar-
retter is cut and the ter-
minals thus formed, -2
and 3, are immersed in
nitric acid, when its sen-
sitiveness is increased
and it will act even more
efficiently than before.
This barretter may be
connected either directly
indirectly with the
or
FIG. 1596.—
FESSENDEX
LIQUID BAR-
RETTER.
FIG. 159a. — FESSENDEN LIQUID
BARRETTER.
vertical wire and ground
as desired. Another meth-
od of constructing a liquid barretter consists in forming a minute
hole through a diaphragm, 7, Fig. 159&, conveniently done
FIG. ItiO. — FES
by drawing down a very thin capillary tube to about ,003 of an
1U. S. Patent 727,331. Receiver for Electromagnetic Waves. Fessen-
den, May 5, 1903.
162 WIRELESS TELEGRAPHY.
inch internal diameter, cementing it into a hole in the center of
a thick glass disk, and then grinding off the ends of the glass tube
until they are flush with the surface of the diaphragm. The dia-
phragm is so arranged in a suitable vessel, 4, as to form a parti-
tion, between two portions of the solution in the cup or holder,
shown at b, so that they are separated except by the thin column of
the liquid contained in the capillary tube which joins the barretter.
There are several modifications of these detectors, but in every case
the vital principles, i.e., "a receiver having a small heat capacity
and consisting of a small quantity of liquid/5 are the same. The
regulation type of Fessenden barretter is shown in the photograph,
Fig. 160.
TESTING BOXES OR BUZZERS. — Makers of wireless telegraph
apparatus furnish with each set a testing box designed for the use
of the operator so that he may instantly ascertain if his coherer
and relay are in working order and poperly balanced for the recep-
tion of messages. With each wireless receptor a half dozen or more
coherers are supplied and, assuming these to have been tested to
insure sensitivity and accuracy, it is only necessary for the operator
to adjust the relay to the resistance of the detector and the current
of the cell included in the local circuit. This adjustment is made
by a milled screw of the relay which determines the movement of
the armature. To learn the degree of adjustment required the
buzzer is employed.
In a box a buzzer and a dry cell are inclosed and these are
connected in series with a push button arranged on top. When the
test is to be made, the box, which measures approximately 3x4x6
inches, is grasped with both hands at the ends, bringing the push
button directly under the thumb. The box is held immediately in
front of and from 4 to 12 inches away from the coherer; the button
is pressed intermittently, which actuates the buzzer, and the slight
sparks produced between its contacts suffice to send out waves which,
if the coherer and relay are operative, will cause the instrument to
respond and its action may therefore be depended upon for distances
up to 40 miles.
CHAPTER XIV.
TRANSMITTERS.
HISTORICAL.
The history of wireless telegraph transmitters for com-
mercial purposes is necessarily brief. In 1896 Marconi con-
structed the first practical system for the generation and trans-
mission of electric waves1 to a distance. He immediately proceeded
to England, where he applied for a patent. Lodge had
made, prior to Marconi's application of the spark-gap principle,
some purely experimental tests,2 but after its actual application to
telegraphy he again took up the subject, and, recognizing the value
of a properly proportioned oscillator in connection with a reso-
nator, he devised and patented an apparatus3 in 1897 which he
exhibited at the Royal Society Conversazione in 1898.
Slaby and Arco of Charlottenburg, Germany, deduced certain
conclusions and formulated theories for an improved transmitter
employing a closed circuit oscillator, and this was described by them
before the Allegemeine Electricitats Gesselschaft, Berlin, in 1904.4
Marconi constructed an improved transmitter for emitting elec-
tric waves of a predetermined length, and read a paper on his
method before the Royal Institution in 1902.5 Braun fol-
lowed with his compound-circuit oscillator, in which the earth is
eliminated as a factor in transmission of electric wave energy,
the text of which he made public in 1902.6 A new transmitter,
previously described, was designed by Fleming for utilizing a low-
frequency, high-potential alternating current and by stepping it up
by means of an oil-insulated transformer, its potential was raised
Marconi's British Patent. Date of application June 2, 1896; Granted
July 2, 1897.
Exhibited at the Royal Institution, June 1, 1894.
'British Patent to Lodge granted May 10, 1897.
'Syntonized and Multiplex Spark Telegraphy, Dec. 22, 1900.
"Progress of Electric Space Telegraphy. Royal Institution, June 13,
1902.
6Braun, Siemens and Halske Wireless TeHgraph System : Elec. World
(Mid Eng., June 14, 1902.
163
164 WIRELESS TELEGRAPHY
sufficiently to charge a series of condensers, which were then dis-
charged through a spark-gap as usual, and in this manner a dis-
ruptive discharge was obtained without the induction coil and its
interrupter. Fessenden had issued to him a series of United
States patents in August, 1902,1 involving many new principles,
the cfief-d'ceuvre of which is a method for distributing capacity
and inductance instead of localizing these coefficients of the oscil-
lator as in previous systems; for carrying this method into
practice a tuning-grid was designed rendering inductance coils
and condensers no longer necessary. John Stone Stone has had
issued to him a large number of patents embracing a method
for impressing oscillations on a radiator system and emitting the
energy in the form of waves of predetermined length whatever may
be the electrical dimensions of the oscillator; and finally Anders
Bull has invented an electro-mechanical transmitter2 the purpose
of which is to automatically send out prearranged series of wave
impulses for selective wireless messages.3
PRACTICAL.
In the analysis of transmitters it will be observed that there are
three systems of circuits; i.e., (1) a low-voltage direct or alter-
nating current circuit,
which includes a source of
e. m. f., a key, and the
primary of an induction
coil;, (2) a low-frequency,
high - potential circuit.
^> > Q which connects the second-
L ^^ ^> ]_ ary of the induction coil
with the spark-gap of the
high-frequency or wave-
emitting circuit — these are
FIG. 161.— SYSTEM OF TRANSMITTING CIRCUITS. termed internal Circuits
and (3) a high-frequency,
high-potential circuit or oscillator or radiator system, as shown in
Fig. 161. In some of the later transmitters there are more than
Fessenden, Wireless Telegraph Patents, Aug. 23, 1902. Elec. World
and Eng.
2See Chapter XVIII. Syntonization.
Scientific American, Mar. 21, 1903.
TRANSMITTERS. 165
three circuits, but those indicated in Fig. 161 are the funda-
mental circuits and additional ones represent transforming circuits
either for frequency or potential.
CLASSIFICATION OF TRANSMITTERS. — Transmitting apparatus
may be divided into two general classes :
A. — Non-syntonized transmitters ;
B. — Syntonized transmitters ;
and these classes may be further subdivided as follows :
C. — Oscillators for high-frequency currents;
D. — Oscillators for low-frequency currents;
Class C may be again divided into two sub-classes :
E. — Oscillators with grounded arms ;
F. — Oscillators with ungrounded arms ;
and these classes and sub-classes may comprise the following
features :
a. — Generators of the induction coil type;
6. — Generators of the transformer type;
c. — Spark-gap connected in series with its aerial wire and
ground ;
d. — Oscillators operating through transformers;
e. — Oscillators with open circuits ;
/. — Oscillators with closed circuits;
g. — Oscillators with compound circuits ;
h. — Oscillators with non-tuned circuits;
t. — Oscillators with tuned circuits;
j. — Transmitters electrically syntonized, and
Ic. — Transmitters mechanically syntonized.
Letters in the text are not indicated in the diagrams, since
these do not relate to the specific parts of the emitter, but
to the nature of the apparatus. The word tuned designates an
oscillator so proportioned that its electrical dimensions correspond
exactly to the frequency of the oscillations set up in it, and the term
syntonized indicates that the coefficientalof the oscillator are of the
same value as that of the resonator operated in conjunction with it.
166
WIRELESS TELEGRAPHY.
In all cases the circuits of the oscillator systems will be shown
diagrammatically and drawings of the internal circuits will be
given where the plans have been available.
MARCONI TRANSMITTER (FIRST FORM). — In the provisional
British Patent applied for by Marconi entitled Transmitting Elec-
trical Signals, and dated June 2, 1896, two forms of transmitters
are covered in the specifications. In the first
form, shown in Fig. 162,1 the diagram indi-
cates that the apparatus is non-syntonized
(A) and the oscillators are not grounded
(F) ; it is operated by an induction coil (a) ;
the oscillator is of the closed-circuit type
(/) and is non-syntonized (h). The fea-
ture of this transmitter is the placing of
the oscillator balls forming the spark-gap
in the focus or focal line of * parabolic
mirror — as in Hertz's experiments — di-
rected toward the receiver. In this transmitter there is no ver-
tical wire or earthed terminal. The distance to which messages
could be sent was so limited that the method
is not now employed.
MARCONI TRANSMITTER (SECOND FORM). —
The second form of transmitter devised by
Marconi is embodied in the patent specifica-
tion above referred to and involves the funda-
mental principles utilized in all transmitters
employing a disruptive discharge. It consists
of a non-syntonized radiator (A) for high-
frequency currents (C), having one arm
grounded (E) ; it is operated by an induction
coil (a) with its oscillator balls connected
with an aerial wire and ground (c), forming
an oscillator of the open-circuit type (e), which is non- tuned (h).
The internal and oscillator circuits are shown in Fig. 163 diagram-
matically, and photographically in Fig. 164. This is the first
recorded instance of an aerial wire and a grounded terminal being
connected in series with a spark-gap, and constitutes an invention.
'Paper by Marconi on Wireless Telegraphy. Inst. of Elec. Eng.
\
MITTER. (Second Form.)
TRANSMITTERS.
167
LODGE TRANSMITTER (FIRST FORM). — In a. British patent
granted to Lodge, May 10, 1897, and one issued to him in the
FIG. 164. — MARCONI SYSTEM.
"1
United States for a similar device dated August 16, 1898, is
described for the first time a syntonized system (B) utilizing the
coefficients of capacity, inductance,
and resistance. In the Lodge
transmitter, Fig. 165, a radiator
consisting of a pair of capacity
areas, 1, 1', made of plates of metal
in the form of cones and having
a definite and uniform capacity are
connected with syntonizing induc-
tance coils, 5, 5', made of a single
layer of wire or metal ribbon pro-
viding the necessary inductance to
effect the proper balance for a
given capacity, and oscillations of
a given periodicity are thus set up.
The disruptive discharge takes
FIG. 165.— LODGE TRANSMITTER. , , 0 , ,, ... ~.
(First Form.) place at 3 and the oscillations are
prolonged to a certain extent ; con-
densers, 4, 4', are inserted in the oscillator circuit, rendering the pro-
168
WIRELESS TELEGRAPHY.
WWWW
m
cess of tuning easier of accomplishment. The internal circuit in-
cludes a battery, a key, and the primary of an induction coil.
The frequency of the oscillations may be varied by increasing or
decreasing the size of the apparatus, and therefore the values of
inductance and capacity. This places the apparatus in the class
of syntonized transmitters (B) and having an oscillator for high-
frequency currents (C) with ungrounded arm or terminal (F) ;
the different parts of the transmitter are characterized by an in-
duction-coil generator (a) supplying
energy to an open-circuit oscillator (e)
and having tuned (i) and syntonized
circuits (j).
SLABY-ARCO TRANSMITTER (FIRST
FORM). — The transmitter of Dr. A.
Slaby and Count Arco, shown in dia-
gram in Fig. 166, was the first form
devised by them. One arm of the
oscillator is grounded; a spark-gap,
2, and a condenser, 3, are in series
with the aerial wire, 1, with a choke ;
coil, 4, intervening between the aerial
wire, 1, and the return conductor, 5,
which also leads to earth; the vertical
wire, 4, is tuned to the frequency of the
oscillations set up in it and the wire, 5,
should be one-fourth the length of the
emitted wave; then if oscillations of any other frequency than
those producing complete waves or four times the length of the
vertical wire occur, they will either find their greatest amplitude
in the coil, 4, or be dissipated in the earth at 5, and in either case
they will fail to emit effective waves. The internal circuits are
not shown. The oscillator system described was designed as a
{^ntonic transmitter (B) utilizing high-frequency oscillations (C)
.and having grounded arms (E) ; it is operated by an induction
coil (a), and the oscillator spheres are in series with the aerial
wire and ground (c) as is the return conductor connected through
the inductance coil forming a closed circuit (/), the whole pro-
ducing a tuned system ({). The difficulty with this transmitter
FIG. 166. — SLABY-ARCO TRANS
MITTER. (First Form.)
TRANSMITTERS.
169
lies largely in placing the choke-coil, 4, between the aerial wire, 1,
and the return conductor, 5, since it has been shown that a closed
circuit is a very feeble emitter.
SLABY-ARCO TRANSMITTER (SECOND FORM). — The new form
devised by Dr. Slaby and his collaborator, Count Arco, contain
the principles of a new theory evolved by them.1 The internal
circuits are shown graphically in Fig. 167, in which 1 represents the
FIG. 167. — INTERNAL CIRCUITS SLABY-ARCO TRANSMITTER.
inductor of a Ruhmkorff coil connected with a mercury turbine
interrupter, 2, driven by a small motor, 3, the number of revolutions
being regulated by the resistance, 4. Connected in parallel with
the turbine is a high-potential condenser, 5, a Morse key with
magnetic blowout, 6, to prevent the fusing of the platinum con-
tacts by heavy currents, and a resistance, 7, for regulating the cur-
rent flowing in the inductor. The terminals 8, 8', connect the
inductor with the source of current. A conductor represented by
the arrow leads to earth and forms a lightning arrester to protect the
1Syntonization. Chapter XIX.
170 WIRELESS TELEGRAPHY.
apparatus from lighting should it strike the aerial, and is also use-
ful in equalizing the high differences of potential between the appa-
ratus and the ground. The oscillator system consists of the second-
Fio. 168. — EXTERNAL CIRCUITS SLABY-ARCO TRANSMITTER.
ary terminals of the induction coil, 1, Fig. 168 ; the oscillator balls
forming the spark-gap, 2, are immersed in oil, and the terminals
are connected with the binding post, and one
of these in turn is connected with the aerial
wire, Af through a battery of Leyden jars, 9,
and the tuning coil, 10. A well-insulated wire
connects the spark-gap with the plug-plate, 12,
which forms contact with the battery of Leyden
jars, consisting of three, seven, or fourteen jars
placed in a cylindrical pasteboard box with the
tuning coil wound on the outside as shown ; Fig.
169 shows a simple diagrammatic arrangement
of the oscillator system with the spark-gap, 2,
connected with the earth at 3; the aerial wire,
4, leads to the earth, 7, through the tuning coil,
5, the battery of Leyden jars, 6, connecting with
4, on one side and the inductance, 8, and
The transmitter is of the
FIG. 169.— GRAPHIC
RERRESENTATION OF
SLABY-ARCO TRANS-
MITTER.
the aerial wire,
spark-gap, 2, on the opposite side.
TRANSMITTERS.
171
syntonized class (B), with oscillator for high-frequency currents
(C), which is grounded (E) ; its generator is an induction coil (a)
oscillator (g) and having tuned (i) and syntonized circuits (/).
Fio. 170. — SL.ABY-ARCO SYSTEM.
its oscillator is connected with the aerial wire and ground (c), and
is a compound circuit (g) formed of an open-circuit oscillator (e)
and a closed oscillator system (/), both of which are tuned to the
period of oscillation (i) and synto-
nized with its complementary reson-
ator system (/). The complete ap-
paratus is shown in Fig. 170.
GUARINI TRANSMITTER (FIRST
FORM). — A new form of wireless
telegraph transmitter employing al-
ternating currents of low frequency
and high potential was tried by
Emile Guarini Foresio, of Brussels,
Belgium, in his experiments in re-
peating wireless messages, and is in
several respects similar to the one
patented by Edison in 1888. This transmitter consists of an ordi-
nary induction coil, 1, Fig. 171, with a mechanical interrupter. The
oscillator, or more properly alternating system for radiating the en-
FIG. 171. — GUARINI TRANSMITTER.
(First Form.)
172
WIRELESS TELEGRAPHY.
ergy, is connected direct to the terminals of the secondary coil and
includes an aerial wire, 2, and the earthed terminal, 3 ; there is no
s.park-gap, but in other respects it follows closely the design of os-
cillators of the open-circuit type. The coil is operated by a 12-cell
storage battery, and the current thus derived is led to a switchboard
and thence through a voltmeter, ammeter, and variable resistance,.
FIG. 172. — GUARINI TRANSMITTER. (First Form.)
to the primary winding of the induction coil. Since there is
no spark-gap, there can be no high-frequency currents, but instead,
there is a surging of the current through the aerial and ground
wires the frequency of which is low, taking place synchronously
with the make and break of the interrupter when the transmitter
TRANSMITTERS.
173
is in action. This transmitter was employed by Guarini at his
Brussels Station. It is shown in Fig. 172. It will be seen that
it is a non-syntonized transmitter (A) having an oscillator for
lowr-frequency currents (D). and utilizing
the earth (E) ; it is operated by an in-
duction coil (a) and its radiator is con-
nected with the opposite terminal (c] ; it
is of the open-circuit type (e), non-tuned
(A).
GUARINI AUTOMATIC TRANSMITTER
(SECOND FORM). — The transmitter Gua-
rini employed in his repeater is similar
to Marconi's second form, but has a con-
denser placed parallel with the spark-gap
to diminish the normal length of the
FIG. 173. — GUARINI
TER.
-GUARINI TRANSMIT- spark and obtain a heavier discharge. The
(Second Form.) £
diagram, Fig. 173, depicts the general
arrangements. The induction coil gave a maximum spark of 25
FIG. 174. — (JuAiuxi REPEATING TRANSMITTER.
cm. with a current of 3 amperes and 30 volts, but during the oper-
ation of the transmitter the spark was cut down to 5 mm. Classified,
174
WIRELESS TELEGRAPHY.
this transmitter is non-syntonized (A), and has a high-frequency
oscillator (C) with a grounded arm. It likewise is operated with
an induction coil (a) and its oscillator is in series with its aerial
wire and ground (c) ; it is of the open-circuit type (e), non-tuned
(h), and non-syntonized. Fig. 174 shows the automatic re-
peater in half tone.
MARCONI TRANSMITTER (THIRD FORM). — In a selective system
patented by Marconi and described by Fleming in the Journal
of the Society of Arts, January 4, 19011,
and shown schematically in Fig. 175, the
inventor has introduced a compound open
and closed circuit oscillator system which
produces the maximum penetrative effi-
cacy of the emitted wave with its maxi-
mum persistency of oscillation. Marconi
employs two copper cylinders instead of
the usual aerial wire. The interior cylin-
der, 1, is connected to the earth at 3 ; sur-
rounding the cylinder 1 is a cylinder, 2,
having a larger diameter and mounted in
such a manner that an air-space insulates
them from each other. The exterior cylin-
der is connected to one side of the spark-
gap, 4, and the interior cylinder to the opposite side of the
spark-gap; the cylinders represent a definite capacity which is
balanced by the variable inductance, 5. In action this trans-
mitter resembles a Ley den jar of gigantic capacity and having
a closed circuit; when a disruptive discharge takes place between
the spark-balls, 4, the high-frequency currents flow through the
compound circuits, surging many times before they are damped
out by transformation into electric waves which retain in a small
measure the strength of those propagated by the open-circuit oscil-
lator, and this factor added to the persistency of the emitted waves
places it in the class of syntonized transmitters having oscillators
for high-frequency currents (C) with a grounded arm (E) ; in this
transmitter an induction coil (a) is used with the oscillator con-
nected in series with the ground (c), the system combining an
open circuit (e) with a closed circuit (/), forming a compound
oscillator (g). The oscillator is tuned (t) and syntonized (/)
World and Eng., Nov. 9, 1901. Syntonic Wireless Telegraphy.
FIG. 175. — MARCONI TRANS-
MITTER. (Third Form.)
TRANSMITTERS.
175
BRAUN TRANSMITTER. — A diagrammatic arrangement of the
transmitter designed by Braun is shown in Fig. 176. It con-
sists of the internal circuits, A, including the primary and sec-
ondary windings of the inductor and the open and closed oscil-
lator circuits, B. In the internal circuit a modified Wehnelt
electrolytic interrupter designed by Simon is used, or where a
low-voltage current only is available a mercury turbine interrupter
is employed. A special key is inserted in the primary circuit capa-
ble of breaking up a current of 50 amperes into dots and dashes
without danger. The secondary terminals, 2, are connected to
-either side of the spark-gap. The closed-circuit oscillator consists
of a series of miniature Leyden jars arranged in two sets of twenty
tubes each and connected in series with the spark-gap and primary
FIG. 176. — BRAUN TRANSMITTER.
winding of a transformer which also acts as an inductance. The
secondary of the transformer is connected with two conductors, 6, 6',
both of which are one-fourth the length of the emitted wave, the
whole forming an open-circuit oscillator one of which serves as the
aerial wire emitting long powerful waves.
The lower conductor, 6', is usually wound in a coil, but having
the same electrical dimensions as the aerial wire, and in order to
eliminate the earth as a factor this conductor is attached to a capa-
city area such as a metal cylinder.1 When in action the persistent
oscillations produced in the closed oscillator circuit are transformed
to any potential desired through the transformer, setting up in the
open-circuit oscillator system a practically constant amount of
Serial Wires and Earths.
176
WIRELESS TELEGRAPHY.
energy, giving rise, therefore, to pure sine waves. This transmitter
is of the syntonized class (B) with high-frequency circuits (C),
which are not grounded (F) ; an induction coil (a) is used to trans-
form the current in the first cycle of operations. A distinct open-
circuit (e) and a closed-circuit (/) forms a compound circuit
FIG. 177 — BRACK-SIEMENS AND HALSKE SYSTEM.
oscillator (g), the operation taking place through a transformer (d) ,
and these are tuned (i) and syntonized (;) for selective signaling.
A photographic view of the Braun-Siemens and Halske system is
given in Fig. 177.
MARCONI TRANSMITTER (FOURTH FORM). — The fourth system
devised by Marconi to solve the problem of syntonic wireless teleg-
TRANSMITTERS.
177
raphy resulted in the arrangement shown in Fig. 178. In assembling
the apparatus for fulfilling the conditions required by theory it is
necessary that the closed-circuit (B) and the open-cir-
cuit (C) should be tuned to the same period of oscil-
lation— or, as Marconi terms it, octaves. Unless these
conditions of the coefficients are fulfilled the different
periods of the (B) and (C) oscillators will set up cur-
rents each of a different frequency and phase, with the
result that these will conflict, and in so doing energy
will be wasted and enfeebled
waves will result. The object
of the variable inductance A in
the open-circuit, then, and the
condenser, e, is to enable the
adjustment of the two circuits
so that they will have the same
natural periods and the cur-
rents in them will be in the
FIG. 178,-MARcoNi TRANSMITTER. same phase. The classification
of this transmitter places it in
the syntonic class (B), having oscillators for high-frequency cur-
rents (C) with one arm grounded (E). An induction coil (a) is
FIG. 179.— POPOFF-DUCREPET TRANSMITTER.
used to charge the oscillator, which is connected in series with the
radiator and ground (c) ; the open-circuit (e) and closed-circuit
178
WIRELESS TELEGRAPHY.
(/) oscillators operate through a transformer (d), forming a com-
pound circuit (g). The oscillators are tuned (i) and the trans-
Fio. 180. — DE FOREST TRANSMITTER.
mitter syntonized (/) for actuating a complementary syntonized
receiver.
PopOFF-DucRETET TRANSMITTER. — The transmitter designed
by Ducretet as the complementary apparatus for PopofFs receptor
is shown in Fig. 179 and is of the ordinary induction coil, open-
circuit oscillator type, similar to Marconi's second form of sending
instrument. The spark-gap is inclosed in the box, o, the induction
181. — DEFOREST TRANSMITTER.
coil is represented at Bo, the motor operated mercurial break at /,
and the key for making and breaking the primary coil at M.
DEFOREST TRANSMITTER. — The DeForest transmitter is shown
TRANSMITTERS. 179
in diagram in Fig. 180 and in half-tone in Fig. 181. The trans-
mitter is based on Fleming's design and employs a primary alter-
nating current instead of a direct current, and a transformer instead
of an induction coil. In Fig. 180 an alternating-current generator, 1,
working at 500 volts, supplies energy to an oil-insulated transformer,
3. which converts it to a pressure of 25,000 volts at the secondary
terminals ; a key, 2, serves to break up the primary current into the
Morse code ; the terminals of the secondary connect with the spark-
gap, 6, of the oscillator system, which comprises the vertical wire,
4, the earthed terminal, 5, and the condensers, 7, 8; in action the
Fio. 182. — FESSENDEN TRANSMITTER.
high-potential currents charge the condensers 7, 8, and these dis-
charge through the spark-gap, 6. This scheme eliminates the in-
terrupter of the induction coil type of generators and gives a heavy
discharge between the spark-balls. This transmitter is in the non-
syntonized class (A) with a high-frequency oscillator (C), and
grounded arm (E) ; generator of the transformer type (b) and
oscillators connected with the aerial wire and ground (c) having an
open circuit (e) and non- tuned circuit (h). It is at once a simple
and a powerful radiator of electric waves.
FESSENDEN TRANSMITTER. — Fessenden has invented a trans-
mitter that is constructed with special reference to tuning, speed
in transmission and economy of operation. It is shown in the dia-
gram Fig. 182 and in the photograph 183. In the diagram 1 repre-
sents a source of e. in. f., 2, a spark-gap, 3, an induction coil which is
kept constantly in action; 4, a non-inductive resistance, 5, a con-
180
WIRELESS TELEGRAPHY.
denser, 6 and 7, tuning girds formed of one or more movable contacts
to each pair of wires which are immersed in oil. The tuning grid
embodies novel features, combining as it does a variable inductance
and capacity without resorting to either coils or condensers; the
grid is simply
formed of parallel
wires, the oil having
a high dielectric ca-
pacity. As it is a
syntonic emitter, it
belongs in the (B)
class, and has a
high-frequency os-
cillator (C) with
grounded arm (E) ;
j an induction coil
| generator (a) sup-
| plies a high-poten-
| tial current to the
1 oscillator in series
| with aerial and
°§ ground wire (c),
o forming an open-
current system (e)
tuned (i) and syn-
tonized (;'). By ad-
justing the grid any
frequency of oscilla-
tion within range
of the instrument
may be obtained.
POPP - BRANLY
L'VHHI^^^V^ TRANSMIT TEE.
— The transmitter
designed by M. Vic-
tor Popp and Prof. Eduard Branly, of Paris, is shown in Fig.
184 ; it consists of an induction coil placed end-on in a case with the
secondary terminals leading to a spark-gap as shown; one side of
the spark-gap is connected to the aerial wire and the opposite side
TRANSMITTERS.
181
leads to earth. The terminals of the primary coil are connected
to a mercury turbine interrupter operated by a small motor. The
FIG. 184. — POPP-BRANLY TRANSMITTER.
transmitter is of the non-syntonized type (A) with oscillator for
high-frequency currents (C) having a grounded arm (E). Its
1S2
WIRELESS TELEGRAPHY.
generator is an induction coil (a), the spark-gap of which is con-
nected with an aerial wire and ground, forming an open-circuit
oscillator (e), which is non-tuned (h).
CERVERA TRANSMITTER. — A transmitter designed by Senor
Julio Cervera Baveria1 for the Spanish government is shown dia-
grammatically in Fig. 185; its chief
feature is an oscillator system in
which the radiating wire is of exceed-
ingly small diameter,, the capacity of
which is increased by connecting in
series, on opposite sides of the spark-
gap condensers, 2, 2' ; it has been
shown that a fine wire will radiate all
the energy it can be supplied with.
A switch is provided for throwing in
the condensers when the transmitter
is in operation and cutting them out
when the receiver is connected to the
aerial and ground wire. A keyboard
similar to a typewriter keyboard was
used in conjunction with the trans-
mitter, and when a key, corresponding
to the letter to be sent, is depressed,
dots or dashes in the Morse code re-
sulted and the impulses they represent
were transmitted. It is a simple non-
syntonized emitter (A) with high-
frequency oscillator (C), and having
a grounded terminal (B) ; an induction coil (a) charges the oscilla-
tor formed of a spark-gap connected in series with its vertical wire
and ground (c), constituting an open-circuit system (e), non-tuned
(h) and non-syntonized.
LODGE-MUIRHEAD TRANSMITTER. — In the new Lodge-Muirhead
commercial system2 two forms of oscillator systems have been used
and these are modifications of Lodge's original transmitter. In
Fig. 186 a spark-gap, s, is connected in series with the aerial wire a,
and having a variable capacity in the form of a condenser interposed
^Electrician (London), April 18, 1902. Wireless Telegraphy in Spain.
Guarini.
2Elec. World and Eng. Lodge-Muirhead System, Collins, Aug. 1, 1903.
FIG. 185.
TRANSMITTERS.
185
FIG. 186. — LODGE-MDIR
HEADTRAN8MITTER.
(First Form.)
at x ; the opposite arm includes the inductance coil, i, a condenser, x,
and grounded terminal, E ; this system may be supplied with energy
by means of an ordinary induction coil or the condensers may be
I a charged by the secondary current of a com-
JL mercial transformer, when they will dis-
V 1 charge through the spark-gap. The com-
pound oscillator system, Fig. 187, comprises
an open and closed circuit ; the aerial wire, a,
in this case is connected with the earth
through the primary of a high-potential
A transformer and a condenser x ; the secondary
1{JX coil forms a closed circuit in which is in-
* eluded a pair of oppositely disposed con-
densers and the primary of an induction coil
or a transformer operated by a commercial
alternating current; the oscillator spheres are in shunt with the
closed circuit. The system shown in Fig. 186 is syntonized (B)
with oscillator for high-frequency currents (C), and has one
arm grounded; a generator of the induction coil type (a) or of the
transformer type (b) may be used; the aerial wire and ground are
connected with the spark-gap, c, forming an oscillator of the open-
circuit type (e), which is tuned (i) and
syntonized (j). The compound oscilla-
tor is in the (B) class, i.e., syntonized
with high-frequency oscillator (C)y
which is grounded (E) ; an induction
coil (a) or transformer (b) may be em-
ployed, and the spark-gap, aerial wire,
and ground are in series (c), forming
'l|]Xl an oscillator of the compound type (</),
I operating through a transformer (d) ;
both the open-circuit oscillator system
(e) and the closed-circuit system (/)
are tuned (i) and syntonized (;'). A Morse key, automatic machine,
and perforator are used in connection with the low-tension circuits,
and the local circuit includes a "buzzer," the purpose of which is
to open and close the primary circuit of the induction coil so that a
definite frequency is obtained. The photograph, Fig. 188, is an
excellent illustration of the Lodge-Muirhead system.
FIG. 187. — LODGE-MUIRHEAD
TRANSMITTER. (Second Form.)
184 WIRELESS TELEGRAPHY.
BULL TRANSMITTER. — The Bull transmitter1 is an electro-
mechanical device designed especially for selecting wireless teleg-
raphy. Its oscillator is of the non-syntonized class (A), designed
for high-frequency currents (C), and has a grounded arm (E), as
in other simple systems/It employs an induction coil (a) energizing
the aerial wire and earthed terminal, forming the oscillator (c),
which is of the open-circuit type (e), non-tuned (/t), but with its
mechanical devices the transmitter is mechanically syntonized.
MARCONI TRANSATLANTIC CABLELESS TRANSMITTER. — The first
cableless signal transmitted across the Atlantic Ocean was emitted
by an enormous plant developing energy equivalent to twenty-five
FIG. 188.— LoDGE-MumuEAD SYSTEM.
horse power and installed at Poldhu, Cornwall, England. The com-
mercial cableless station erected at Tablehead/ Glace Bay, Nova
Scotia, is equipped with a generator connected to a forty horse-power
engine and the one at South Wellfleet, Mass., develops one hundred
horse-power. In these great transmitters the engines are coupled
with alternating-current dynamos generating electricity at a pres-
sure of 2.000 volts, which is then converted by oil-insulated trans-
formers to a potential of 100,000 volts; a battery of oil condensers
is constantly charged by this high-voltage current, and these dis-
charge through a spark-gap formed by the terminal of the aerial
and the ground wire. Thus the designing of long-distance trans-
mitters has been resolved into a comparatively simple engineering
task involving the transformation of low-potential, low-frequency
currents into high-potential, high-frequency oscillations,
^yntonization, Chapter XIX.
CHAPTER XV.
RECEPTORS.
HISTORICAL.
The first complete receiving and indicating device for electric
waves was not applied to wireless telegraphy, but for meteorological
determinations. In 1888 Hertz obtained calculations at a distance
of a few feet with his ring detector. Lodge in 1894 showed how a
coherer connected with a galvanometer could be used as a receiver
when placed a distance of 500 feet from the source of the waves.
Prof. Popoff, of Cronstadt, designed a receptor for the study of
atmospheric electricity in 1895, and this arrangement forms the
earliest record of the application of an aerial wire or antenna con-
nected with a detector and the earth. Prof. Rutherford, of Mont-
real, in 1896, constructed a magnetic detector and with suitable
auxiliary appliances forming a receptor obtained signals at a dis-
tance of 2,500 feet.
In his experiments in Italy, Marconi in 1895 employed a coherer
with one of its conductor plugs connected with an elevated capacity,
the opposite terminal of the detector being earthed.1 The first tests
b)r Marconi, in England, in 1896, were, however, executed without
recourse to the antenna and earthed wire, but by concentrating the
received waves in the focus of a parabolic mirror containing the
detector. From the records it seems that Marconi was the pioneer
in utilizing the Morse register in combination with a detector and
relay. The history of wireless telegraph receptors is analogous to
that of transmitters, since in nearly every case inventors of trans-
mitters designed complementary apparatus for the reception and in-
dication of the waves; thus Lodge gave to the world the first
syntonic receptor or resonator simultaneous with his tuned trans-
mitter (1898), the result being a complete syntonic system of
wireless telegraphy. Upon the discovery that carbon and some of
the metals were self-restoring, the telephonic receptor came into use.
Wireless Telegraphy, Marconi. Institution of Elec. Engs. , March 2, 1899.
185
186 WIRELESS TELEGRAPHY.
The Slaby-Arco and Braun systems of Germany, the Popoff-Decretet
of France, and other makers use this type of detector in combination
with telephone receivers for portable receptors. Fessenden's barret-
ter is an auto-detector, as is the DeForest electrolytic responder.
Marconi's cableless stations are equipped with telephonic receptors,
and the signs of the time point to its ultimate adoption as the
successor of the Morse register type. An electro-mechanically oper-
ated receptor for wireless telegraphy has been constructed by Anders
Bull and is the latest addition to the art.
PRACTICAL.
The term receptor will be used where it is intended to designate
a complete receiving apparatus. Receivers refer to individual parts
of receptors such as telephone receivers, et cetera. Receptors com-
prise two principal circuits, i.e., (1) a milli-ampere, low- voltage
JL direct-current circuit shown at 1, Fig.
j . t 189, operating a relay or telephone re-
*• "• , ceiver, af by means of the cell, b, through
' " " * the detector, c, and (2) a high-frequency
circuit which includes the aerial wire, 2,
2. detector, 2', and grounded terminal, 2";
upon this circuit the electric waves im-
pinge, when they are transformed into
-" R 3 electric oscillations. The first w termed
an internal circuit, and the second a resonator system. There may
ibe one or more internal circuits and more than one resonator system,
but the two. circuits indicated in the diagram are the principal ones.
CLASSIFICATION OF RECEPTORS. — Receptors may be divided into
the following classes :
A. — Non-syntonized receptors.
B. — Syntonized receptors.
And these classes may be again indicated thus:
C. — Resonators with grounded arms.
D. — Resonators with ungrounded arms.
E. — Receptors with visual recorders.
F. — Receptors with telephonic receivers.
These classes may consist of the following appliances :
a. — Detectors operated by voltage.
b. — Detectors operated by current.
RECEPTORS.
187
c. — Resonators connected in series with antennas and grounds.
d. — Eesonators operating through transformers.
e. — Resonators of the open-circuit type.
/. — Resonators of the closed-circuit type.
g. — Resonators of the compound-circuit type
h. — Receptors with non-tuned circuits.
i. — Receptors with tuned circuits.
/. — Receptors electrically syntonized.
Jc. — Receptors mechanically syntonized.
Combinations of these various factors make up a great variety
of receptors differing widely in detail, arrangement and specific
purpose, yet all are dependent on the same sources of energy for
their operation.
POPOFF RECEPTOR. — The receptor designed by Popoff in 1895
consisted of a coherer, 1, Fig. 190, one terminal of -which was con-
CLtCfRIC BtLL
•BKTTtRY
Fio. 190. — POPOFF RECEPTOR.
nected to an exploring rod, 2, or antenna, as it is now termed, the
opposite terminal, 3, leading to the earth through the coherer and
spark-gap, 4 ; these oppositely disposed coherer terminals were con-
nected in series with a relay through a cell, 5, and in an auxiliary
circuit there was included a bell, the tapper of which served also
188
WIRELESS TELEGRAPHY.
to decohere the filings.1 Thus the first actual long-distance receptor
may be classified as a non-syntonized system (A) with a resonator
having one terminal grounded (C) ; though no Morse register was
used, it had all the elements of the (E) type, except the register it-
self. The apparatus in the internal circuit was actuated by a voltage-
operated detector (a) of the coherer type, and this was connected in
series with the antenna and ground (c), forming an open-circuit
resonator (e), the whole comprising receptors with non-tuned
circuits (h). The Popoff receptor formed the foundation for those
of every system since devised where Morse registers are used.
MARCONI RECEPTOR (FIRST FORM). — The earliest form of re-
ceptor designed by Marconi is shown diagrammatically in Fig. 191.
PIG. 191.— MARCONI RECEPTOR. (First Form.
It consisted of a coherer, jf f-f ;2, ;3, connected with a polarized
relay, n, and a dry cell, g, in series with the non-inductive resistances
or choking coils, fc1, fc1, so that the sparking of the contacts of the
relay which sets up oscillations in the local circuit may be anni-
hilated or "choked" before they reach the coherer, and again these
choking coils compel the oscillations set up in the resonator system
to traverse the coherer instead of wasting their energy in following
the alternative path which includes the relay. Non-inductive re-
sistance coils are also inserted in shunt at q and s, so that there may
be no electrical disturbances by the local battery near the coherer,
which otherwise would retard the detector in regaining its high
resistance after the action of the oscillations. The relay causes
the current from the battery, r, to pass through the tapper, p, and
'Elektritchestvo, St. Petersburg, July, 1896.
RECEPTORS.
189
also through the electro-magnets of the sounder, li. The tapper or
decohering device is adjusted so that it will tap back the filings to
their normally high resistance; when the impinging waves on the
resonator system are converted into oscillations the coherer permits
the current to flow through the circuits, and this causes the deli-
cately poised armature of the relay and tapper to vibrate rapidly
and in unison with each other; when the coherer closes the circuit
the relay armature is drawn into contact, and, closing the second
local or internal circuit, starts the tapper ; the tapper in turn, by
decohering the filings, stops the action of the current and the
operation of the relay. In the sounder first employed and the
Morse register since used, the levers are arranged to have a high
time constant compared with the armatures of the relay and tapper,
and the former, in virtue of its great inertia, cannot, therefore,
follow the rapid movements of the latter, so that when a series of
waves are received representing a dash in the Morse code the arma-
ture or lever of the recorder remains down until the cessation of the
LFic. 192. — MARCONI RECEPTOR. (Second Form.)
waves ; a dot is registered in the same way, but, the waves being of
shorter duration, the lever is held down a shorter time. In this
receptor a parabolic reflector was employed to receive the impinging
waves and concentrate them upon a small resonator formed of
copper plates, Jc Jc ; it was designed to be used in connection with the
Marconi transmitter (Fig. 162). It will be observed that it is in
the class of non-syntonized receptors (A), having an ungrounded
190 WIRELESS TELEGRAPHY.
arm (D) and employing a Morse register (E). The indicator is
operated by a voltage detector (a) of the coherer type, and the
resonator is of the closed-circuit type (/), the circuit of which is
non-tuned (h). Theoretically, the choke coils, k ~k, place the res-
onator in the open-circuit class (e), but the general design is that
of a closed-circuit system. All receptors giving visual indications
by means of Morse registers are constructed upon practically the
same lines as the one just described.
MARCONI RECEPTOR (SECOND FORM). — In the second form of
receptor designed by Marconi and shown in Fig. 192, the resonator
system is formed by an antenna extending into the air and supported
by a mast, balloon, or kite, one terminal of which is connected to
the coherer, the opposite conductor plug forming connection with
the earth at E. An open-circuit resonator is thus obtained and
practice has indicated this to be best adapted to the requirements
of long-distance wireless telegraphy. The arrangement of the tapper
FIG. 193. — MARCONI INSTALLATION AT BABYLON, L. I.
with the extra choke-coils, p*, p2, are here represented together with
the additional connections required to complete the equipment; in
all other respects the receiver is the same as that just described.
In the photograph shown in Fig. 193 it will be observed that the
RECEPTORS.
191
apparatus is inclosed in a metal box ; the object oi this arrangement
is to preclude extraneous waves from impinging on the wires of the
internal circuits and thus set up oscillations and miniature trains
of waves.
LODGE RECEPTOR. — Early in the art Lodge, recognizing the
importance of sending and receiving selective messages, designed
a system to fulfill these requirements. The receptor illus-
trated in Fig. 194 consists of a resonator sys-
tem for the reception of electric waves of a
definite length and converting them into os-
cillators of a given frequency. In nearly all
receptors the resonator is merely a counter-
part of the oscillator or complementary ap-
pliance, having about the same electrical
proportions as the oscillator system with
which it is so closely allied. The resonator
system employed by Lodge is made by con-
necting two capacity areas, 1, 14, together by
an inductance coil, 6; this inductance also
serves as the primary coil of a small trans-
former, the secondary, 7, of which is con-
nected in series with the coherer, 8. The re-
cording apparatus is similar to that shown
in Fig. 192. The capacity areas are of metal, either zinc or copper,
and are cone-shaped. This receptor is in the syntonized class (B)
and the post, 9, insulates the capacity areas
from the earth so that the resonator is un-
grounded (D). A Morse register (E) indi-
cates the message, through a voltage-oper-
ated detector (a) ; the resonator has two cir-
cuits operating through a transformer (d) ;
utilizing the properties of both the open-
circuit (c) and the closed-circuit resona-
tors (/) and giving it a compound char-
acter (g) ; these circuits are not only tuned
(i), but syntonized (/).
SLABY-ARCO EECEPTOR. — The Slaby-
Arco multiple- tuned receptor is based on a
number of original conclusions bearing on
FIG. 195.-SJABT-ARCO RE- ^ ^ Qjf electpical resonance. In Fig.
FIG. 194. — LODGE RECEP-
TOR.
192
WIRELESS TELEGRAPHY.
195, the antenna is shown at 1, leading to the earth at 2. A second or
auxiliary wire representing the same inductance, capacity, and re-
sistance as the antenna is connected with it at the point of contact
with the earth or nodal point; in the receptor the wire terminates
in the coherer, the opposite terminal leading to earth through
the condenser. The internal circuits are shown in Fig. 196; the
fcl _____ I?
i;
J Hii ^rth
FIG. 196. — INTERNAL, CIRCUITS.
antenna is connected with the relay as indicated by the dotted lines,
while the heavy lines illustrate the circuit which includes the relay,
tapper, and Morse register; 1 is the antenna, 2 a cut-out, and 3, 4,
5, 6, and 11 the circuit comprising the resonator. The relay, 8,
is operated by the cell, 9, which leads through the magnets of the
tapper, 10, to the coherer, 5, the circuit being completed through
the inductance, 4, and the coil connected with the earth terminal,
11, the return leading to the relay. The second internal circuit
includes the battery, 12, the tapper, 13, the relay working contact,
14 — including the tongue — the polarizing battery, 15, the elements
of which are connected in parallel, and the Morse register, 16.
The resistance of the Slaby-Arco coherer is about 2,000 ohms and
the relay is wound to about the same resistance; it is of the
Siemens polarized type. The receptor is syntonized (A) with
grounded-arm resonator (C) and operates a Morse register (E) ;
the coherer (a) is connected in series with the antenna and ground
(c) and has resonators of the open circuit type (c) and closed
circuit type (/) both of which are tuned (i) and syntonized (/).
BRAUN KECEPTOR. — The resonator system of the Braun receptor
RECEPTORS.
193
is shown in Fig. 197, in diagram. The antenna, A, upon which the
waves impinge sets up oscillations in the closed resonator formed by
the condensers, c, e, and the inductance coil, t, which also acts as
FIG. 197. — BRAUN RESONATOR.
the primary of a small transformer coil. The addition of a second
conductor, B, equal to y the received wave, gives the proper elec-
trical symmetry to the primary open circuit, whereby pure resonance
FIG. 198. — BRAUN RELAY, TAPPER AND COHERER.
effects are obtained. The second conductor, B, instead of being
grounded as is ordinarily the case, is a short piece of wire attached
to a cylinder which acts as a capacity replacing both the wire and the
194
WIRELESS TELEGRAPHY.
earth itself in so far as the coefficients of either are concerned.
The polarized relay, the tapper, and coherer are clearly shown in
Fig. 198 ; the relay is of the Siemens type with permanent magnets,
the magnet coils of which are wound to high sensitiveness. The tap-
per differs from those of electro-mechanical construction in that it is
merely actuated and not operated by an electric current, its energy
being imparted by a spring motor. The Braun receptor involves the
principles of the syntonized class (B), the resonator system is un-
grounded (D), and the receptor indicating the message by means
of a register (E) ; it employs a coherer (a) and its resonator
operates through a transformer (d) ; the resonators follow the
e, f, g classes in that they are open, closed and compound; the
circuits are tuned (i) and syntonized (;'). A Braun portable
receptor is illustrated in Fig. 199.
i IG. 199. — BRAUN PORTABLE RECEPTOR.
MARCONI KECEPTOR (THIRD FORM). — In the effort to eliminate
the antenna as a factor in the reception of electric waves, Marcom
evolved a third form of apparatus, shown in Fig. 200. The recep-
tor consisted of two concentric cylinders of metal with an air-
space between them. The inner one is connected with the earth ;
the outer one is connected to the inner one by a circuit which
includes the primary of a transformer coil of special design and
a coil for varying the inductance. The capacity is constant and is
RECEPTORS. 195
determined by the size of the concentric cylinders. The secondary
of the transformer coil forms a closed-circuit resonator with a
coherer and a relay in circuit. It follows
the syntonized class of receptors (B), the
resonator has a grounded arm (C) and util-
izes a Morse register (E) ; a coherer (a) is in
the closed resonator circuit and the inner
cylinder connected with the earth places it in
the (C) class; the resonator operates through
a transformer (d) and is of the compound
type (g) ; both circuits are tuned (i) and
syntonized (;').
GUARINI AUTOMATIC REPEATER. — A
wireless telegraph repeater combining in a
single instrument a transmitter and a re-
FIG. 200.— MARCONI RE- ceptor is the invention of Emile Guarini
CEPTOR. (Third Form.) r .
Foresio; the repeater is absolutely auto-
matic in all its functions, and from the instant the en-
feebled radiation from a distant station impinges on the
antenna through all the succeeding translations from the coherer
to the powerful re-energized waves emitted from the same aerial
wire no human hand is required to assist it. Fig. 201 is a diagram
of the combined circuits representing the receptor and the trans-
mitter/and Fig. 202 is a photograph of the complete apparatus.
A single vertical wire, 1, serves to receive and radiate the waves;
a special switch, 2, provides the means for automatically cutting
out the aerial wire from the spark-gap, when the receiving ap-
paratus is brought into action and vice versa. The inductor, 3,
supplies current to the oscillator; a condenser, 4, is shunted
across the spark-gap as previously described. The receptor con-
sists of a Siemens relay, 5, placed in series with a Blondel regen-
erable coherer, 6 ; the platinum surface contact points of this relay
are too small to transmit the current required to operate the induc-
tion coil, so a second relay or aerial switch, 2, having a larger
carrying capacity, is used. The aerial wire is connected directly to
one terminal of the primary winding of a transformer coil, 7, the
•opposite terminal leading to earth through the metal box, 12 ; the
coil, 7, increases the potential of the oscillatory current in the
coherer circuit, in which is included a condenser, 8, serving the
'Guarini's Transmitter, 2d form, Chap. XIV.
190
WIRELESS TELEGRAPHY.
purpose of establishing the proper ratio between inductance and
capacity.
Non-inductive resistance coils, 9 and 10, are inserted between
the relay, 5, and the coherer, 6; to protect the internal circuits,
including the relay and coherer, the whole is inclosed in a metal
box, 12, and as an extra precaution a choking coil, 13, is intro-
Fio. 201. — GUARINI AUTOMATIC REPEATER
duced to annihilate any oscillations set up in the circuit connecting
the aerial relay, 2, and the polarized relay, 5. The action of the
repeater is such that when the incoming waves are received, oscil-
lations occur in the open-circuit resonator system formed by the
antenna, 1, one side of the relay, 2, the metal box, 12, and the wire
leading to earth; the waves acting on the coherer, 6, close the
circuit of the relay, 5, which in turn causes the armature of the
aerial relay, 2, to be drawn into contact, switching out the resona-
RECEPTORS. 197
tor circuit and switching in the radiator system when the re-
energized waves are emitted. The oscillator and resonator circuits
are virtually a unit of the non-syntonized type (A) having a
grounded arm (C) ; the message is received by a Morse register
(E). The coherer places it in the (a) class, the former being in a
closed resonator circuit, operating through a transformer (d)
FIG. 202. — GUARINI AUTOMATIC RKPEATER.
having a compound-circuit resonator (g) ; the receptor is non-
tuned (h). This system of repeating wireless messages was tested
between Antwerp and Brussels, a distance of 25 miles.
MARCONI EECEPTOR (FOURTH FORM). — The fourth type of
receptor devised by Marconi for selective wireless signaling is
shown in the sketch Fig. 203. An aerial wire, A, is connected
to earth, Ef through the primary of a transformer, j1, and the
198
WIRELESS TELEGRAPHY.
Pro. 203. — MARCONI RECEPTOR.
(Fourth Form.)
variable inductance, g\ the secondary coil of the transformer is
connected in series with the coherer, Tf and the free terminals of
the secondary a condenser, f, the op-
posite coatings of which connect with
a source of e. m. f., and a relay. The
condenser increases the capacity of
the closed-circuit resonator system,
and in the case of a prolonged series
of comparatively feeble but properly
timed oscillations being received they
are stored up until the e. m. f . at the
terminals of the coherer is sufficient
to break down its high resistance and
cause the indicating apparatus to re-
spond in consequence1. The trans-
former is especially wound and is de-
scribed in the succeeding chapter.
Classified, this resonator is of the
syntonized type (B), having a
grounded arm (C), the receptor in-
cluding a Morse register (E) ; a coherer (a) operated through
a transformer (d) connects an open-circuit resonator (e) in
series with antenna and ground (c) with a closed-circuit sys-
tem (f), forming a resonator of the compound-circuit type (g) ;
these resonator circuits are tuned (i) and syntonized (/). This
system was tested between St. Catherines, Isle of Wight, and
Poole, in Dorset, England. When electric waves of a certain
frequency are used no interference is caused by the working of the
Admiralty installations in the vicinity.
FESSENDEN KECEPTOR. — The receptor devised by Fessenden
embodies several novel and important features. Its resonator
system is closely allied to the oscillator system, since a specific
tuning device serves either purpose. The resonator system, of
which the tuning devices form the principal part, is shown in Fig.
204, and has for its object the reception of code messages and others
where accuracy and positive action are essential. The antenna, 1,
is connected through a condenser, 12, with one of the tuning grids,
13 ; this device is connected with the wave detector or barretter, 14,
'Royal Institution Lecture, Progress of Electric Space Telegraphy. Mar-
coni, June 13, 1902.
RECEPTORS.
199
the resonator circuit being completed through the tuning grid, X,
which leads to earth E. The tuning grids are constructed of one
or more pairs of conductors arranged in a box containing oil in-
sulating the wires. By this arrangement the capacity and induc-
tance of the circuit is distributed, instead of bunching these
coefficients by coils and condensers, which tends to cut down the
effective radiation per oscillation.
Fio. 204. — FESSENDEN SYSTEM.
The barretter of Fessenden is connected in series with a pair of
head telephone receivers, 15, and current is supplied by a pair of
elements having a slightly opposed e. m. f., through a non-induct-
ive resistance. The diagram Fig. 204 shows a complete send-
ing and receiving apparatus; 20 to 25 is an electro-magnetic
cut-out, and this device is rendered operative through the switch,
200
WIRELESS TELEGRAPHY.
a, b, 3, the lever, 25, drawing the leading-in wires, 24, in or out
of contact as the case may be. The calling apparatus is shown in
32, and comprises a coherer, 35, a transformer 33 and 34, a tele-
phone receiver, a bell or other suitable indicating mechanism. The
Fessenden receptor is subject to the following classification: It is
^ syntonized receptor (B) with grounded arm resonator (C) using
a telephone receiver to indicate the signals; its detector is current
operated (&), and is connected in series with the antenna and earth
(c), forming an open-circuit resonator ('e) ; which is tuned (i) and
syntonized (/). The photograph Fig. 205 shows the new type of
FIG. 205. — FESSENDEN SYSTEM.
liquid barretter and other features of the system. Fig. 206 is a
portable Fessenden apparatus.
PopOFF-DucRETET RECEPTOR. — Like the Popoff-Ducretet trans-
mitter, the receptor designed by them resolves the receiving appara--
tus into its simplest form, i.e., a single cell, a detector, and a tele-
phone receiver. When in action the coherer, A, is attached to the
top of a containing box or case, and connection with the dry cell
and telephone is made by means of a flexible cord and spring jacks.
The coherer, containing grains of carbon, decoheres automatically,
•so that no tapper is required. The aerial wire is connected to one
"terminal of the coherer and the earthed wire to the opposite ter-
RECEPTORS.
201
minal. It is simply a non-syntonized receptor (A), having a
grounded resonator (C) using a telephone receiver (F) as an indi-
cator, actuated by an auto-coherer (a) connected in series with
the antenna and ground (c), forming an open-circuit resonator1
(e) and non-timed (h). It is shown in Fig. 207.
DEFOREST-SMYTH RECEPTOR. — The receptor illustrated dia-
grammatically in Fig. 208 and photographically in Fig. 209 is the
result of researches by Dr. Lee DeForest and Edwin H. Smythe;
FIG. 206. — FESSENDEN PORTABLE EQUIPMENT.
it employs as a detector an anti-coherer based on electrolytic prin-
ciples, which responds to the impressed differences of potential in
a manner diametrically opposite to that of a coherer. Usually two
fesponders, as these detectors are termed, are connected in series,,
as shown in the diagram, with the antenna and grounded terminal ;
1, I1 represent the responders, 2, 21 choking coils, 3 an inductive
resistance, 4 a source of e. m. f., 5 a condenser, 6 a head telephone
receiver, 7 the antenna, 8 the ground wire, and 9, 9 cut-outs for
the responders. The internal circuit includes the head telephone
receivers, responders, and cells; the internal circuit is normally
closed, the current flowing through the telephones all the time the
202
WIRELESS TELEGRAPHY.
anti-coherer is not actuated by the oscillations; when the oscilla-
tions take place, however, the latter disrupts the electrolytically
deposited thread formed by the local current between the electrodes
of the responder, when its resistance is instantly increased, the local
current ceases to flow, and the diaphragm of the telephone receiver
released from the pull of the magnets recovers its normal position,
producing a sharp click. This receptor is of the non-syntonized
class (A), has a grounded resonator (C), and utilizes a telephone
receiver (F), its detector is voltage-operated (a), the resonator is
FIG. 207. — POPOFF-DTTCRETET RECEPTOR.
connected in series with the antenna and ground (c), is of the
open-circuit type (e), and is non-tuned (h). Messages have been
received at the DeForest Coney Island station from the Etruria,
when the steamer was ninety miles at sea.
CERVERA EECEPTOR. — The receptor of Senor Julio Cervera
Baveria1 operates through the same aerial and ground wire as the,
transmitter, but the condensers employed for the latter are cut out
by means of a switch. The construction of the receptor is shown
In the diagram, Fig. 210 ; and, it will be observed that the antenna^
1, is connected with the earthed terminal, 2, through the primary
coil of a small transformer, 3; in the secondary of the transformer,
Electrician. London. April 18, 1902, p. 1008. F;Vr;!;
RECEPTORS. 203
4, is inserted a condenser, 5; the soft iron core, which is also in
circuit with the secondary, terminates in the coherer, 7 ; a variable
resistance, 8, is included in the local circuit, connecting the co-
herer and the relay, 10, and the cell, 9;
the battery, 11, is thrown into circuit by
the relay, 10, which operates a second or
multiplying relay, 12. The battery oper-
ating the Morse register is shown at 13,
while 14 is the de-coherer battery and 15
the tapper. The sensitiveness of the co-
herer may be regulated through the wind-
FIG. 208.-DSFORE8T REC7p- inS of the electro-magnet and the resist-
TOIU ance, 17; a battery for regulating the
electro-magnet, 18, is also inserted in this circuit as well as an
ammeter, 19. There are, consequently, four distinct circuits in this
receptor, each having its own source of current and fulfilling the
following functions: (a) actuating the Morse register, (b) making
and breaking the coherer and relay circuit to render decohesion
more positive, (c) operating the tapper, and (d) interrupting the
circuit of an electro-magnet regulating the coherer. The receptor of
Cervera is non-syntonized (A), with grounded resonator (C), and
the receptor indicates its message by means of a Morse register
(E), it employs a coherer (a) operating through a transformer (d),
forming a compound resonator (g) having non-tuned circuits (h).
The device is quite complicated, but has been in operation between
Tarifa and Ceuta across the Strait of Gibraltar, a distance of 34
kilometers.
BRANLY-POPP RECEPTOR. — The principal feature of this system
is the Branly tripod coherer, previously described. This coherer is ar-
ranged at the back of the Morse register, Fig. 211, so that a lever
operated by the latter serves as a tapper for the detector, thus elim-
inating the electro-mechanical tapper usually employed. The local
current from the cell, B, which has an e. m. f . of one-half volt, actu-
ates the spring motor of the register through an internal circuit
formed through the screw, A, in the lever referred to, making con-
tact with a platinum plate, P, leading to a Claude relay, R, the cir-
cuit being completed through a variable resistance, v, and the tripod
coherer, D ; the terminals leading from the relay connect with the
Morse register. The receptor is non-syntonized (A), the resonator
having one arm grounded (C), the message being indicated by a
204
WIRELESS TELEGRAPHY.
Morse register (E) ; its detector is of the coherer type (a) and its
resonator formed by a direct connected aerial wire to the coherer
and ground (c) of the open-circuit type (e), and is non-tuned
(h). The Branly-Popp system is in operation between Cape Gris
FIG. 209. — DEFOREST RECEPTOR.
Nez and Cape de la Hague. The half-tone, Fig. 212, gives an excel-
lent idea of the completed receptor. In Fig. 213, the receptor is
shown connected to recording meteorological gauges which are now-
being used in France..
LoDGE-MuiRHEAD KECEPTOR. — In the new Lodge-Muirhead re-
ceptor1 two distinct resonators have been tested. The first is a
*Elec. World and Eng., Aug. 1, 1903, p. 173. Collins.
RECEPTORS.
205
simple open circuit, and the second is a compound-circuit system.
The open-circuit resonator comprises an antenna, a, Fig. 214, lead-
Fio. 210. — CERVERA RECEPTOR.
ing to the earth through the condensers, x and x± ; the internal cir-
cuits include an inductance, L, a Lodge rotating mercurial coherer,
WIRELESS TELEGRAPHY.
C, condenser, X2, and a siphon recorder operated by a current from
the cell, E. No relay is interposed between the coherer and the
recorder, rf the action being direct. This receptor is syntonized (B),
and, different from the first Lodge system, has a grounded resonator
(C), it employs a siphon recorder (E), and a voltage-operated
detector (a) is placed in a shunt with the internal circuit of the
resonator proper, the aerial wire being connected direct to the
earth with the condensers interposed (c) ; the resonator is of the
open-circuit type with tuned resonator and internal circuits (i)
producing a syntonized receptor (j).
The compound-circuit oscillator, shown in Fig. 215, is com-
posed of an open-circuit resonator, a, primary of a transformer, tpf
FIG. 211.— BRANLY-POPP RECEPTOR.
which also serves as an inductance and condensers, xlf and x2 ; the
latter connecting with the earth ; the secondary of the transformer,
ts, is in series with the rotating mercurial coherer, c, forming a
closed circuit including a cell, E, and a siphon recorder, r; in
shunt with this circuit is a condenser, x2, causing the oscillations
to surge through the closed circuit with a predetermined frequency
until it reaches its maximum amplitude, and excluding these oscil-
lations from the recorder.1 The complete receptor is illustrated
in Fig. 216; the latter A refers to the siphon recorder, B the
actuating mechanism, D reversing switch, E voltmeter, and F
the transformer. When properly adjusted for sending a message
the needle of the recorder is sustained so that if a dash is trans-
mitted a long line is recorded on the. tape, while a dot is indicated by
British Patent, Lodge and Muirhead. No. 20,069.
RECEPTORS.
207
a short line. In actual practice the lines may waver, but absolute
accuracy is not of importance, as it is just as easy for an operator
to translate the recorded script even though there are a number of
impulses to each dash. Its fine adjustment is not, however, diffi-
cult, but every minute fluctuation of the recorded impulses may be
easily noted and the fault traced at once to the transmitter or re-
ceptor, as the case may be, and rectified; Fig. 217 is a reproduction
of a tape of the siphon recorder. The experimental stations of the
Lodge-Muirhead system were located at the works of Muirhead &
Co., Elmer's End, Beckingham, Kent, and at Downe, eight and
one-half miles distant, with the intervening geological formation
FIG. 212. — BRANLY-POPP RECKPTOR.
of Kentish chalk which offers five times the amount of resistance
of the sea, and the distance, therefore, representing about 44 kilo-
meters.
BULL EECEPTOR. — The receptor designed by Anders Bull con-
sists of an open-circuit resonator for mechanically receiving wire-
less messages, and will be treated in the chapter on Syntoniza-
tion. It is a syntonized receptor (B) with resonator, having
one terminal grounded (C), and employs Morse registers; de-
tectors of the coherer type (a) are placed in series with antenna
and the ground forming a resonator of the open-circuit type (/),
the circuits of which are non-tuned (h), but the receptor is
mechanically syntonized (Tc).
•MARCONI TRANSATLANTIC CABLELESS RECEPTOR.— The first
signals transmitted across the Atlantic Ocean wirelessly from
208
WIRELESS TELEGRAPHY.
Poldhu, Cornwall, were received and indicated at St. Johns,.
Newfoundland, by an apparatus of extreme simplicity. It con-
FIG. 213. — BRANLY-POPP METEOROLOGICAL APPARATUS.
sisted of an open-circuit resonator formed of a single aerial
wire elevated in the teeth of a storm by a huge Baden-Powell
kite. The free terminal of the improvised antenna was connected
FlG. 214. LODGE-MtTIRHEAD
RECEPTOR. (First Form.)
FIG. 215. — LODGE-MUIPHKAI>
RECEPTOR. (Second Form.)
direct to one of the conductor plugs of a Solari auto-coherer, the
opposite conductor plug leading to earth. In series with the
coherer there was connected a telephone receiver with a single
cell, and all adjusted to a nicety. "S" was the letter translated
RECEPTORS.
209
into the Morse code represented by three dots and sent out by the
Poldhu radiator with an energy equivalent to forty-five horse-
power; three faint clicks were heard in the telephone on the shore
£^Ji-
FIG. 216. — LooGE-MuiRHEAD HECEPTOR.
of Newfoundland, 3,000 miles distant, and cableless telegraphy be-
came a fact. In the more recent receptors for the indication of
cableless messages, a magnetic detector and many other types of
FIG. 217. — TAPE OF A SIPHON RECORDER.
wave responsive devices have been tested. The resonators for
the permanent station equipments are the inverted pyramidal forms
of wires used as radiators, and are tuned and syntonized with the
complementary station with which it is working, so that the best
results may be produced.
CHAPTER XVI.
FIG. 218.— MORSE KEY.
SUBSIDIARY APPARATUS.
The general synthetic arrangement of wireless telegraph sys-
tems, comprising the transmitting and receiving apparatus, ha&
been described in detail, while the individual appliances have been
treated more or less briefly. As
the finished system depends
'argely upon the design, construc-
tion, and proper adjustment of
the various parts, a more com-
plete account may be found use-
"«].
KEYS.
An ordinary telegraph key,
Fig. 218, will serve to arbitrarily
make and break a current of the
requisite energy to operate a
four-inch coil into Morse dots and dashes ; coils • of greater pro-
portions require heavier currents and must be provided with suitable
keys; these are usually modifica-
tions of the regulation type.
MARCONI KEY. — The key
adopted by Marconi for the heavy
service required of it in sending
wireless messages is shown in Fig.
219, and is one in which the lever
and contacts assume much larger
proportions than the ordinary
Morse type. The lever is in-
sulated from the contacts and has
a hard rubber handle set at right
angles to the lever. The stationary and movable brass contacts
are connected in series with a battery and the primary winding
of the induction coil. When the key is operated the handle is
grasped firmly and depressed, a spring producing the reciprocal
210
Fio. 219. — MARCONI KKY.
SUBSIDIARY APPARATUS.
211
action. A condenser in the base of the key aids materially in cut-
ting down the spark formed on breaking the circuit.
(A) BRAUN KEY. — Professor Braun devised a key enabling an
operator to break up a current of fifty amperes continuously with-
out danger to the coil, interrupter, or key itself. The key is so
arranged that the principal contact is made after the circuit is
closed. On breaking the circuit the contact is opened first and
Fio. 220a,6. — BRAUN KEY.
but one path is left for the current, i.e., through the discharger.
By this means the break remains nearly sparkless.
(B) BRAUN KEY. — Another method of preventing the fusion
of contacts is by fitting the key with a magnetic blowout. Fig. 220,
o> b, shows an exterior and an interior view illustrating the posi-
tion of the magnets for blowing out the spark formed on breaking
FIG. 221. — MAGNETIC BLOWOUT.
the primary current between the platinum points of the key. This
device is based on Davy's discovery of the effect of a magnetic
field upon the voltaic arc and its application to other apparatus for
preventing injurious discharges has been the subject of much liti-
gation in the United States in the Thomson magnetic blowout
212
WIRELESS TELEGRAPHY.
suits. Fig. 221 is a diagrammatic view of a blowout applied to a
spark-gap.1 An electro-magnet, NS, is placed with its axis at
right angles to the line joining the contacts, A, B, and produces
a strong magnetic field between
them. The instant the current is
broken the spark is extinguished by
the magnetic field. Instead of the
magnetic field a blast of air may
be used effectively.
DUCRETET KEY. — Ducretet, the
French instrument-maker, devised
the key shown in Fig. 222 ; it con-
sists of two insulated standards
supporting a cup containing mer-
cury ; a spring handle is arranged to
operate freely through the bar con-
necting the standards; the handle
carries at its lower extremity a me-
tallic point; when the handle is
pressed downward the movable
metallic point comes in contact
with the mercury and the primary circuit is completed; when the
handle is released the spring causes it to resume its normal
FIG 222.— DUCRETET KEY.
FIG. 223. — FESSENDEN KEY.
position breaking the circuit formed between the point and the
mercury.
Inventions of Nikola Tesla. Martin, p. 209.
SUBSIDIARY APPARATUS.
213
FESSENDEN KEY. — The time constant of the foregoing keys
is very high, and to increase the speed Fessenden designed the
key illustrated in Fig. 223; to an ordinary Morse steel-lever key
is attached a device for throwing the sending circuit in and out
of tune. This is accomplished by means of the key, 4, which is
FIG. 224. — DE FOREST KEY.
provided with fingers, 10, arranged to be pressed into contact with
the wires so that the circuit is shunted around the tuning grid.
This action takes place in an oil chamber.
DEFOREST KEY. — In the DeForest system an ordinary Morse
key has a curved projecting arm attached to the lever and ex-
FIG. 225.— DE FOREST KEY.
tending into a compartment containing oil; on the lower end
of the arm is a contact having a comparatively small surface and
oppositely disposed to it is a stationary metal contact as shown in.
214
WIRELESS TELEGRAPHY.
Fig. 224. From these contacts well insulated leads connect with
the transformer and generator. Only the manual portions of the
key are exposed and these are thoroughly insulated since the break
takes place under oil. It is illustrated in half-tone in Fig. 225.
FIG. 226. — LODGE-MUIRHEAD KEY AND PERFORATOR.
LoDGE-MuiRHEAD KEY. — In the Lodge-Muirhead system of
transmission a large Morse key1 (see Fig. 226) is usually employed
FIG. 227. — LODGE-MUIRHEAD BUZZER.
in connection with a perforator, a device by which a message may
be prepared at leisure and despatched with celerity. The operation
is simple ; a tape is passed through a perforator with a key attached
lElec. World and Eng., Aug. 1, 1903. Lodge-Muirhead System.
SUBSIDIARY APPARATUS.
to it; by manipulating the
key, the message is punched
in the tape. When it is de-
sired to transmit the mes-
sage, the tape is passed
through the automatic ma-
chine in circuit with the
source of e. m. f., and the
inductor of the coil; the
message may be sent as
rapidly as desired, a brush
passing over the perfora-
tions in the tape, closing the
circuit. In this way speed
and accuracy are attained.
LODGE-MUIRHEAD BUZ-
ZER. — In conjunction with
the key and automatic trans-
mitting machine a "buzzer"
is included in the local cir-
cult; it is shown in the
photograph, Fig. 227, and
in a side elevation in Fig.
228; the object of this de-
vice is to open and close
the primary circuit of the
induction coil so that a de-
finite frequency is obtained
in the local circuit ; the buz-
zer consists of two sounders
connected with each other so
that they operate alternate-
ly. To a copper rod is
fastened an arm of alu-
minum and connects with
the armature of one of the
sounders; the copper rod
has a pointed end dipping
into a cup of mercury and
making or breaking con-
216
WIRELESS TELEGRAPHY.
tact as the lever is drawn up or down; this arrangement inter-
rupts the current about 600 times per minute, so that a similar
frequency is set up in the secondary and electric waves are emitted
at small but definite periods of time.
CONDENSERS.
In oscillator circuits where high-frequency, high-potential cur-
rents surge, condensers having variable capacities are sometimes
desirable, especially in syntonic systems. The Leyden-jar type
of condenser is the simplest in construction and the oil condenser
the most satisfactory, since the insulating properties of oil are very
high while its specific inductive capacity is very low. Experiment
has shown that it is desirable to exclude all matter of a gaseous
|*8
1
hf
FIG. 229 A. B. — TESLA OIL CONDENSER.
nature adjacent to the dielectric in order to prevent electrostatic
bombardment and the untoward effects resulting as a consequence.
TESLA OIL CONDENSER. — An oil condenser designed by Tesla is
shown in the sectional drawings, Fig. 229, A and B. The condenser
plates are contained in a suitable case, A ; the plates, B} C, are
connected to the terminals, D, E, leading outside the case. To pre-
vent the plates from spreading or coming in contact with each other
they are separated by a strip of porous insulating material, F\ the
interior of the case is then filled with the oil, G. This type of con-
denser is highly efficient and will not be affected by high-potential
currents. The capacity of the condenser ma}f be varied within cer-
tain limits by securing the plates to the adjustable rods, H, passing
through stuffing boxes, Kf in the case, A ; the distance between the
plates may be varied by the nuts, LL.
BRAUN CYLINDRICAL CONDENSER. — An adjustable condenser,
composed of a series of miniature Leyden jars so arranged as to
bring within as small a space as possible the greatest capacity area,
SUBSIDIARY APPARATUS.
sir
was devised by Braun for increasing or decreasing the capacity of
his oscillator. The tubes, Fig. 230, are made of glass, have a
diameter of 25 mm., are 2 mm. in thickness, and are coated inside
and out with tinfoil. They vary in capacity from 0.004 micro-
farad to 0.005 mf., and the capacity of the system may be easily
adjusted by merely slipping them in or out of the rack. In this
way the closed-circuit oscillator is tuned to its own natural period
as well as to the open-circuit oscillator emitting the waves.
FIG. 230. — BRAUN CYLINDRICAL CONDENSER.
ADJUSTABLE MICA CONDENSERS. — In resonator systems the po-
tential of the oscillations is very low compared with those emitting
the waves, and the condensers employed may be made with a
dielectric of mica. Mica condensers may be obtained in the open
market in any form, capacity, and adjustability desired. Adjustable
condensers comprise a number of sections, and by a system of
plugs, inserted or removed, the various condenser units may be
thrown in or out of circuit as desired. Non-adjustable condensers
of a given value are often used in resonator systems where the
218
WIRELESS TELEGRAPHY.
capacity of the circuit has been accurately determined, as in the
Braun condenser illustrated at A, Fig. 231.
TRANSFORMERS.
BRAUN HIGH-FREQUENCY TRANSFORMER. — The primary wind-
ing of the high-tension transformer making the electrical connec-
FIG. 231. — BRAUN CONDENSER AND TRANSFORMER.
tion between the open and closed circuits of the Braun oscillator
is designed so that it will give the desired wave length with the
FIG. 232. — BRAUN HIGH-FREQUENCY TRANSFORMER.
greatest capacity. The diameter of the transformer is 20 cm. ; and
is illustrated in Fig. 232, when the various parts are assembled, and
SUBSIDIARY APPARATUS, 219
in Fig. 233 when taken apart. It consists of an inductor of four
turns of heavy wire wound outside of a secondary coil formed of
thirty or forty turns of fine wire, so that oscillations set up in the
closed-circuit oscillator may be stepped up in the open-circuit oscil-
lator emitting the waves. The transformer removed from the jar
shows clearly its internal construction, consisting simply of
an air-core induction coil with the primary well insulated and
its relative position to the secondary reversed; the coils are then
immersed in oil. The transformer of the compound resonator sys-
tem (see B, Fig. 231) is very much smaller than the transformer
above described, since the impressed potential in the resonator
circuit must necessarily be smaller than in the oscillator system.
FIG. 233. — BRAUN TRANSFORMER. (Dissected.)
MARCONI LOW-POTENTIAL TRANSFORMER. — A transformer or
jigger produced by Marconi for his receptor consists of a primary
coil wound with fine wire contrary to custom and the secondary
with still finer wire in single layers.1 It was found that if more
than one layer was employed in the device no results were ob-
tainable ; this was a disadvantage, since a greater number of turns
was required to obtain a higher ratio of transformation between
the primary and secondary than unity, as at A, Fig. 234. To
overcome this obstacle the number of turns of wire on the sec-
ondary was increased at the ends, as shown at B, Fig. 234, and
this transformer giving excellent results, the coil C, Fig. 234, was
constructed. This particular winding prevents the opposition
'Discourse by Marconi, Royal Institution, Feb. 2, 1900.
220
WIRELESS TELEGRAPHY.
effects of electro-magnetic induction with the electrostatic induc-
tion at the ends of tlie primary.
w
FIG. 234a. — MARCONI LOW-POTENTIAL TRANSFORMER.
FIG. 2346. — MARCONI LOW-POTENTIAL TRANSFORMER. (Second Form.)
FIG. 234c. — MARCONI LOW-POTENTIAL TRANSFORMER. (Third Form.)
DE-COHERERS.
Devices for tapping back the filings of coherers to their nor-
mally high resistance are usually of the vibrating type, that is, they
are arranged with an automatic make and break. Single-stroke
tappers have been employed, but are .not well adapted for the pur-
pose. In a properly constructed tapping mechanism the striking
SUBSIDIARY APPARATUS.
221
lever to which the hammer is attached should be short, since it is
desirable to give the vibrating element a low time constant, as this
FIG. 235. — MARCONI DE-COHERER.
is one of the essential features in the production of dashes when
used in conjunction with a Morse register.
MARCONI DE-COIIERER. — In the Marconi tapping device the
FIG. 230. — BRAUN DE-COHERER.
electro-magnets are set at an angle of 45° on a block of wood; the
armature, striking lever, and hammer are arranged beneath, as
WIRELESS TELEGRAPHY.
shown in the photograph, Fig. 235, so that the coherer is tapped
from the under side. The ivory holder with, its coherer attached is
held in position by means of an adjustable ebonite standard, and
the strength of the hammer stroke is regulated to a nicety by screws
controlling the standard, the magnets moving the hammer up
and down.
BRAUN DE-COHERER. — The Braun electro-mechanical de-coherer
is shown in Fig. 236 ; the mechanism for producing the strokes is
FIG. 237.— GUARINI DE-COHERER.
actuated by a local current, but is operated by a spring motor ; this
renders the operation of tapping the tube entirely independent of
the local current. The force is therefore always uniform and the
filings are arranged in the same relative positions each time. When
the filings cohere, a trip catch is released electrically and the
mechanism is set in motion ; when de-cohesion takes place the catch
drops and the motor is stopped. The coherer may be easily and
quickly placed in electrical connection with the internal circuit by
slipping it into place between the opening clutches forming the
contacts.
SUBSIDIARY APPARATUS.
223
GUARINI DE-COHERER. — The de-coherer employed by Guarini
is arranged with a spiral spring and screw, giving a very fine ad-
justment and permitting strokes to be applied to the coherer of any
Tequired strength. The standards for holding the coherer in posi-
tion are rigid, as shown in Fig. 237. It is a simple and efficient
type of electro-mechanical de-coherer.
COLLINS DE-COHERER. — A device to take the place of
the electro-mechanical tapper was designed by the author in
1899. In this arrangement the
coherer is a little different from
those previously described in that
the conductor plugs are beveled,
forming a V-shaped pocket as
shown in Fig. 238; in this are
placed some fine Norway iron fil-
ings carefully annealed to prevent
the retention of magnetism. Over
the tube is an electro-magnet, the terminals of which are connected
in series with the coherer and relay. When the oscillations cohere the
filings the local current energizes the magnet and the particles of
iron are attracted to the polar projection ; this causes the circuit to
be broken, since the resistance becomes infinite as the gap formed
between the plugs gradually widens.
FIG. 238. — COLLINS MAGNETIC DE-CO-
HERER.
RELAYS.
The relay is employed in wireless for the same purpose that it is
in wire telegraphy, i.e., it permits very feeble currents to be aug-
mented by stronger ones. There are two types of relays, (a-)
those having delicately poised soft-iron armatures and (6) those
having permanently magnetized armatures. The former are known
as ordinary relays and the latter as polarized relays. Ordinary re-
lays are wound to resistances of from 50 to 1,000 ohms and polarized
relays are wound to as high as 10,000 ohms. Eelays of less than
1,000 ohms are useful only in the laboratory or for lecture purposes
when applied to wireless telegraphy.
ORDINARY EELAYS. — In wireless telegraphy the relay is usually
connected in series with the coherer and cell. When the filings
cohere, an armature carrying a contact is attracted by the magnets
until the movable contact makes connection with a permanent con-
224
WIRELESS TELEGRAPHY.
tact, when a second or local battery will be thrown into circuit
which operates the tapper and actuates the Morse register. A screw
is provided. for moving the magnets toward and away from the
armature, as may be observed in Fig. 239; so that the proper ad-
justment may be obtained. The armature of soft iron is pivoted
between two set screws. A spiral spring capable of regulation draws
the armature away from the magnets ; there are four binding posts,
two of which are placed in the circuit including the electro-magnets
connecting with the coherer and two in circuit with the local
battery, Morse register and tapper. The differential relay is an-
PIG. 239.— ORDINARY RELAY.
other type employed in duplex and quadruplex telegraphy, but it
has not yet been used in wireless telegraphy.
POLARIZED RELAYS. — The polarized relay, in virtue of its high
sensitiveness, has been adopted by all the leading makers of wireless
telegraph instruments where a Morse register indicates the mes-
sage. The sensitiveness of this type of relay is due largely to the
elimination of the retractile spring common to the ordinary relay,
and another decided advantage of the polarized relay is that its
adjustment, made by means of a single screw, is easily effected and
as easily maintained. In the Marconi polarized relay, in the type of
receptor designed for use on board ship, there is a delicate re-
tractile spring attached to the armature lever to compensate for
the motion of the vessel, but this does not materially affect its
sensitiveness.
SUBSIDIARY APPARATUS.
225
A polarized relay consists of a permanent steel magnet, N, S,
and an electro-magnet., m, m', with the usual soft iron cores; the
lower poles of this magnet are secured to the N pole of the per-
B _ manent magnet, and therefore both of the upper
poles of the electro-magnet, n, ri, will be of the
same polarity as N, provided no current is flow-
ing through the coils, m, ra', but when the co-
herer permits the local current to flow, the N
pole of one of the electro-magnets becomes much
-7/1, stronger, which changes its polarity to the op-
posite sign. A perspective view of the polarized
relay without its casing, is shown in Fig. 240 ;
FIG. 240.— POLARIZED the armature lever, c, c1 ', is pivoted at B and
JVELA.Y.
swings between the poles of the electro-magnets, n, n , but the arma-
ture is adjusted so that it approaches a trifle closer to one pole
than the other, for if it were absolutely equidistant it would not
move, since it would be equally attracted by either pole; the lever
rests against an insulated point, D', Fig. 241, when there is no
FIG. 241. — POLARIZED RELAY. (Top View.)
current, but it is drawn into contact with the point D when the
current energizes the magnets. The contact points are adjustable,
so that the lever may be brought into the proper relations with the
magnets. Braun's polarized relay is illustrated in Fig. 242 and a
standard polarized relay of the Marconi type is shown in Fig. 243 ;
these relays have a high sensitiveness and will operate on one
226
WIRELESS TELEGRAPHY.
twenty- thousandth of an ampere ; by closing the circuit through the
medium of the human body the armature of one of these relays will
•
FIG. 242. — BRAUN'S POLARIZED RELAY.
readily respond if its adjustment is maximum, and this is a method
employed by operators to test its working properties.
INDICATORS.
There are four different means used for the indication and final
translation of the received impulses into a readable alphabet.
Enumerated these are (a) the ordinary telegraph sounder, (b) the
FIG. 243. — MARCONI POLARIZED RELAY.
Morse register, (c) the telephone receiver, and (d) the siphon re-
corder. In the types a and c the messages are rendered audible and
SUBSIDIARY APPARATUS.
227
in b and d they are indicated visually. The sounder has not found
a very wide application, although Marconi once used it, since the
reception of messages where voltage-operated detectors require tap-
ping to restore their resistance necessitates a period of time so great
that deciphering the code by sound becomes exceedingly difficult;
so then a Morse register or a siphon recorder becomes a valuable
adjunct, and, regardless of how slowly messages are received, they
are easily read. The telephone receiver has been utilized for three
reasons: (1) it is the most sensitive receiver known; (2) it will
operate with a current of exceedingly limited variability and will
therefore work with auto-coherers and current-operated detectors
. .... 1:44. MOKSK itlCUlMTKU.
where the changes are not great enough to operate other indicating
devices; and (3) it possesses speed; added to these factors are
others, including durability, simplicity, and cheapness.
MORSE EEGISTER. — This type of indicator is used in nearly all
the receptors designed by English and continental experts in wire-
less telegraphy, since the factor of time does not enter into the
question of reading the etherogram, and besides a permanent record
of the dispatch is obtained. The Morse register is usually an
electrically actuated, mechanically operated device, and in this case
it is self -starting ; in the recently designed Marconi recorders the
mechanism is started by hand. The electrical parts of a recorder
comprise an electro-magnet having an armature connected with the
228 WIRELESS TELEGRAPHY.
spring motor, so that when it is attracted by the magnets the
mechanism is set in motion and a toothed disk draws the paper
tape, supplied from a roll, across a wheel having an inked surface.
The armature is also in connection with the disk, and when a cur-
rent flows through the magnets the inked surface is drawn into
contact with the moving tape and impresses upon it a dot or a dash
as the case may be. The mechanism is controlled by a weighted
vibrating rod and may be regulated so that the paper will move
fast or slow as desired. But the tape should move slowly compared
with the time period of the vibrations of the decoherer tapper, so
that the frequency of the latter produced by the coherer and the
lever of the relay will cause the succession of dots to run together
on the tape and make a continuous mark as long as the armature is
x^.
&
d b c a
FIG. 245.— TELEPHONE RECEIVERS.
attracted to the magnets. Fig. 244 is a photograph of an Ameri-
can-made Morse register.
TELEPHONE EECEIVERS. — The subject of telephone receivers has
been so exhaustively treated that little need be said relating to their
construction. In the ordinary Bell magneto-electric telephone
receiver a coil of fine insulated wire is connected in circuit with the
wave detector and a chloride of silver or dry cell. A permanent
steel bar forms the core for the coil of wire, projecting a few
mm. beyond the ends; a disk of turned or japanned iron called
a diaphragm is supported firmly at its edges, but is capable of
vibrating at its center. Fig. 245 shows a number of different forms
of receivers ; starting from the right, a shows the watchcase form, &
the commercial Bell receiver, c the Swedish type, and d the Collins
wireless telephone receiver.
SUBSIDIARY APPARATUS.
229
SIPHON EECORDERS. — The siphon recorder, invented by Lord
Kelvin for indicating the sluggish and feeble signals from long
cables, has been adapted to the indication of wireless telegraph
FIG. 246. — SIPHON RECORDER.
messages by Prof. Lodge and Dr. Muirhead. In the siphon re-
corder the rise and fall of the local current caused by the variations
of conductivity of the mercury coherer operates through a rec-
tangular coil of very fine wire, b, b', as shown in the outline draw-
FlG. 247. — LODGE-MUIRHEAD SlPHON RECORDER.
ing, Fig. 246; this coil is suspended by thin wires, f, f, between
the poles of a permanent magnet, N, S. A stationary soft iron
core is magnetized by induction and the fluctuation of the cur-
230
WIRELESS TELEGRAPHY.
rent swings the coil from right to left. A fine siphon, one end
of which dips into the ink, projects the latter on a tape moved
by an automatic mechanism, and thus graphically depicts the
curve of the current strength flowing through the circuit. The
coherer circuit is connected with the suspension wires, f, f. In
the Muirhead recorder the ink is discharged from the siphon by
causing it to vibrate. These and other improvements have been
FIG. 248. — SLABY-ARCO TUNING COIL.
added to the original siphon recorder by Dr. Muirhead; the com-
plete instrument is shown in Fig. 247.
TUNING COILS.
In the oscillator of the Slaby-Arco system this is made of a
few turns of heavy, bare copper wire wound concentrically on an
insulating cylinder containing the Leyden jars. Adjustable con-
tacts are arranged so that the value of inductance may be varied at
will. The tuning coil of a resonator system, see Fig. 248, consists
of a number of turns of No. 16 B. and S. gauge wound spirally on
SUBSIDIARY APPARATUS.
231
a cylinder of wood. Each turn represents a length of one meter, and
there are 110 turns, so that the coil may be utilized in tuning any
wave length up to 400 meters.
CHOKING COILS.
A salient feature introduced by Marconi to increase the working
range and accuracy of his receptors are choking coils; the relation
of these coils to the circuits is given in Fig. 249, the object being to
cut off the oscillations surging through the resonator so that the
full value of potential difference may be impressed on the coherer,
as well as to prevent the surging of high-frequency currents in the
closed internal circuit, which would result in the emanation of
trains of electric waves and a reaction of the coherer. Choking coils
Fio. 249. — CHOKING COIL IN CIRCUIT.
are also placed in the second internal circuit, which includes the
tapper and the recording device, so that oscillations set up due to
the capacity of the circuits will be annihilated before resultant deter-
rent electric waves can be set in action. Choking coils are placed in
various parts of the internal circuits and the accuracy of indication
is greatly improved. Fig. 250 is a full-size illustration of a choking
coil; the coils consist of a given length of wire dovbled back on
itself and then wound on a wooden spool so that both ends terminate
on the outside of the spool, forming a non-inductive coil ; these coils
have an approximate resistance of 4,000 ohms and are wound with
silk-covered wire No. 40 B. & S.
POLARIZED CELLS.
Polarized cells are used in the Slaby-Arco and some other sys-
tems instead of the choking coils introduced by Marconi, the ob-
ject of which is to prevent sparking of the relay contacts and so
232
WIRELESS TELEGRAPHY.
eliminate the detrimental waves thus set up. A polarized cell con-
sists of a small vessel containing dilute sulphuric acid, in which a
pair of platinum wire electrodes are immersed; a battery of four
or five of these cells is connected in series across the relay contacts.
SCREENING CASES.
In practice it is usual, where voltage-operated detectors are
used, to place the different parts of the receptor, i.e., coherer, tapper,
battery, and rela}r, on a common base, which is then inclosed in
Fio. 250. — MARCONI CHOKING Con,.
a metal case to protect them from the heavy discharges of the near-
by transmitter. These cases should be grounded so that oscillations
set up in them may be dissipated in the earth.
ALPHABETIC CODES.
There are a number of codes used in telegraphy, the principal
ones being the American Morse and the Continental alphabets.
The latter is best adapted to the purposes of wireless transmission,
since there are no spaced letters ; twelve to fifteen words per minute
is sufficiently rapid where a Morse register is employed and twenty-
five to thirty words per minute is about the speed limit where a
telephone receiver is used.
SUBSIDIARY APPARATUS.
I
233
CONTINENTAL WIRELESS TELEGRAPH CODE.
.»- _l
.&.
.5.
I ./_
- .JS.
• ••••
...
./..
)••••• «••• MiiT** UJ"J5^IAND DOJ^T^ UNDERSTAND
PERIOD INTERROGATION EXCLAMATION
INTERROGATION
• • tm mm ••
12
»••••••• • •••••••
ft 7
•••»•• !••••••
• — — — • — •^L
34
•••••• •••••
9
•••• •••••IBB*
MORSE WIRELESS TELEGRAPH CODE.
A
B
C
•• •
D
E
•
F
G
H
1
••
J
— •«— •
K
L
M
N
0
• •
P
• ••«.
Q
R
• «•
S
•••
T
U
•• —
V
•••••
W
X
Y
z
a
1
2
3
•••—••
4
«...—
PERIOD
«*^ ^ ••
INTERROGATION
5
6
••«•••
7
8
— •«•€
COMMA
EXCLAMATION
9
0
COLON
SEMICOLON
•••••
CHAPTER XVII.
AERIAL WIRES AND EARTHS.
HISTORICAL.
In a patent granted to Thomas A. Edison, dated December 29,
1891, means are shown for transmitting signals without wires by
elevating plates of metal on poles or by balloons. The aerial wire
was connected to one terminal of a secondary coil with the
opposite terminal leading to the earth; while this is perhaps
the earliest reference to aerial wires and earth plates, the
method does not employ either a* spark-gap or a wave detector for
oscillatory currents. In Amos E. Dolbear's patent, issued in 1886,
no reference is made to the elevation of the capacities he suggested
for the equalization of the coefficients of the circuit connected with
the earth. In 1895 Isadore Kitsee obtained a patent for signaling
without wires and indicated how one terminal of the system was
extended vertically to an elevation approximating the height of a
vessel's mast. The antenna and earth utilized by Prof. Popoff in
his meteorological receptor in 1895 and that by Marconi in his
electric wave transmitter, the patent application of which was filed
in England in 1896, are the earliest references to the subject of
aerial wires and grounds in connection with electric wave wireless
telegraphy. In Nikola Tesla's British specification, filed October
21, 1897, he describes a method of producing "a very high electrical
pressure, conducting the current caused thereby to earth and to a
terminal at an elevation." The various designs for aerial radiators
and antennas employed in different systems will be treated in
sequence in the text appertaining to their application in practice.
THEORETICAL.
There are two theories relating to the probable capacity of the
earth and several concerning the role the earth plays in the operation
and propagation of electric wave signals. The true solution of the
234
AERIAL WIRES AND EARTHS. 235
problems presented by the earth is practically the key to syntonic
wireless telegraphy. In one of the two theories referred to the earth
is considered as a sphere insulated in space ; the second and opposi-
tion theory assumes the earth with its surrounding envelope of air
to be a condenser. Koepsel1 by a formula in electrostatics for the
potential of a charged sphere insulated in space deduced a result
showing the earth's capacity to have a low value and comparable
with artificial capacities used in wireless telegraph practice.
The second theory advocated by the author treats the earth
and air as if they were two concentric spherical shells,
the medium between them representing its specific inductive
capacity, when their capacity will be the same as in the
case of two parallel plates with their surfaces brought in
close proximity with each other in the form of a condenser. If,
as the first theory postulates, the earth is a single spherical shell
insulated in space, its capacity must necessarily be very limited,
since a single coating on a glass jar would be incapable of acquiring
more than the slightest charge ; but if the strata of atmosphere holds
a charge opposite to that of the earth, then it may be likened to a
complete Leyden jar with its inner and outer coatings, and its
capacity would be enormously increased. The importance of know-
ing absolutely the capacity of the earth cannot be overestimated, but
could such conclusions be thus positively ascertained, the density of
the charge at a given point could only be taken as a theoretical
standard ; for, owing to the differences of atmospheric densities, the
electric charge may be maximum or minimum at any point at any
given instant, and even then of a different sign.
Many different views have been submitted to explain the relation,
if any, of the earth to the radiating and receiving systems ; among
the more prominent may be mentioned the following: (a) that high-
frequency currents are projected from the earthed terminal of the
oscillator, whence they are conducted by the earth to the resonator ;
(&) that the earth acts simply as a local capacity for the aerial
wires; and (c) that the earth as a capacity having a large value
serves to tune the oscillator and resonator, since both being grounded
would represent the same capacity. As to the nature of the earth
as a conducting medium for electric waves there is also a variance
of opinion; by those advocating sliding waves the sea is regarded
as opaque to electric waves, and it is claimed that in this it fulfills
'Koepsel, Dingler's Polytechnisches Journal, June, 1903.
236 WIRELESS TELEGRAPHY.
Maxwell's law in that salt water is a conductor of electricity.
Others voice the opinion that the sea will transmit electric waves,,
since salt water does not follow the general law for conductors, in
that it conducts by electrolytic action. One fact, however, is
positively known, namely, that electric waves are much more
easily transmitted over salt water than over fresh water or land.
Whatever these conditions may be, it is well known that if a
metallic conductor, as a lightning rod, be extended upward
in the air and its lower terminal connected with the earth, a con-
stant current will flow through it, equalizing in a small measure
a difference of potential that is always present. If this conductor is
divided and the resulting terminals form an air-gap, the potential
difference may be measured by a galvanometer, or if the air-gap is
microscopic in size sparks will pass ; if a detector of the coherer type
is inserted in the gap the filings will cohere under certain meteoro-
logical conditions and the restoration of the charge will be indicated.
In practice these atmospheric disturbances often produce characters
on the tape of the recording instrument, and these untoward indi-
cations are called "X's," or stays. The purpose of the aerial wire,,
on the one hand, is to send out transverse vibrations in the ether in
the form of electric waves, and on the other, to receive them; it
was ascertained by Dr. Slaby and Prof. Braun that the proper
length of the aerial wires should be one-fourth the length of the
emitted wave, and therefore the radiator and antenna should have
as nearly the same height as possible.
A law relating to the distance over which electric waves may be
transmitted with a given height of aerial wire was deduced em-
pirically by Marconi very early in the practice of the art. This
law states that with a given current, instruments of standard di-
mensions and all other factors being equal, the distance to which
signals may be transmitted increases as the square of the length
of the radiating wire ; or, graphically, if a wire 20 feet in height will
transmit one mile, a wire 40 feet in height will send waves four
miles, and one 80 feet in height will transmit waves sixteen miles,
et ccetera. This general law was mathematically evolved by Prof.
Ascoli, who deduced his conclusions in accordance with Neu-
mann's formula and found the reciprocal action to be propor-
tional to the square of the length of one of the two aerial wires
if these are of equil length, and in simple inverse proportion of the
distance between them.
AERIAL WIRES AND EARTHS.
237
It would seem that the empirical law of Marconi and the
deductions of Ascoli may be subject to modification since Captain
Bonomo, of the Royal Italian Navy, has concluded that the dis-
tance to which signals may be transmitted is in accordance with
the formula L = 0.15 ^/"^ where L represents the length of the
aerial wires, D the signaling distance in meters and 0.15 is a con-
stant. Where a number of parallel wires are employed instead
of a single vertical wire as first used by Marconi this apparent
discrepancy is accountably due to a greater radiation of energy
and also in virtue of a longer wave length emitted.
The intensity of the oscillations does not diminish with the
•30
20
40 CO 80 100
Distance In Kilometers
120 140
Fio. 251. — CURVE OF ELECTRIC WAVE RADIATION.
increase of distance if the length of the aerial wires is increased 'in
proportion or as the square of the distance ; therefore, by doubling
the height of the aerial wires the distance of signaling may be four
times as great. In a series of experiments carried out by Dr. Slaby
to determine with precision the exact height of aerial wire required
to transmit messages over a given distance the curve shown in Fig.
251 was plotted. Starting with an initial energy of 746 watts, the
curve represents the maximum distance for transmission over bodies
of salt water, with the Slaby- Arco standard station apparatus. Con-
siderable latitude has been allowed for meteorological and climatic
changes and unfavorable conditions of the year, as, for instance,
the heated atmosphere of the summer months. The accuracy of the
curve has been tested carefully, and while the sending and receiving
238 WIRELESS TELEGRAPHY.
instruments are calibrated in accordance with the curve, their
actual working distance may be much greater, as, for instance, it was
found possible to obtain messages between the Deutschland and
Duhmen, a distance of 150 kilometers, whereas the curve gives the
working distance as 80 kilometers. The photo-electric effect of sun-
light on aerial wires was deduced by Marconi1 based upon the con-
clusions reached by Hertz2 in 1887, who found that the effect of one
electric spark from an induction coil on another had a tendency to
diminish the size of the latter, and that this curious result was due
to ultra-violet radiation — in which the disruptive discharge is
rich — dissipating the charge of electricity stored in the second oscil-
lator system. Eighi attributed the effect to the ultra-violet radia-
tion producing convection or the process of dispersing negative
electricity, the charge being carried away by the molecules of air.
Bighi3 also determined that ultra-violet radiation charged wires,
when insulated, with positive electricity, and Elster and Geitle have
been able to show the dissipating influence of not only sunlight, but
of diffused daylight on conductors. This phenomenon was observed
at the antennas by Marconi when he received signals a distance of
2,099 miles from Poldhu, Cornwall, England, on the steamship
Philadelphia. During the test made on this trip it was ascertained
on one occasion that the signals were distinct and clear at night for
2,000 miles, but in daylight the signaling distance was only a fourth
as great, or 500 miles.
PRACTICAL.
In practice it is of vital importance to maintain absolute in-
sulation of the aerial wires and earthed terminals of the radiator
and resonator circuits, for in utilizing high-frequency, high-poten-
tial currents leakage becomes excessive should any portion of the
systems come in contact with masts, buildings, or other physical
appurtenances. Where the aerial and ground wires are sustained
or supported, heavy glass or porcelain insulators are desirable.
The wires themselves should be highly insulated, since this pro-
tects the oscillatory currents from dissipating their energy in the
atmosphere and does not retard the action of the electric waves,
for insulators are transparent to them.
Progress of Space Telegraphy. Royal Inst. Lecture, Marconi, June
13, 1802.
^Wiedemann's Annalen. 31, p. 983.
*Comptes Rendus, vol. 107, p. 559.
AERIAL WIRES AND EARTHS.
239
METHODS OF SUSPENSION. — A simple and efficient method for
suspending aerial wires from the yardarm of a mast is shown in
Fio. 252. — SIMPLE METRO
OF SUSPENSION.
Fio. 253. — DUCHETET METHOD
or SUSPENSION.
Pig. 252 ; the mast is represented at 1, the yardarm 2, insulator 3,
capacity area 4, and wire 5. The insulator is supported by a loop
FIG. 254.— BRATTN LEADINO-IN METHOD.
of tarred rope attached to the yardarm, and the capacity area, or
wire if it be used direct, is inserted longitudinally in the insulator
240
WIRELESS TELEGRAPHY.
as shown. The method illustrated in Fig. 253 was designed by
Ducretet and is a superior modification of the one just described.
A method to eliminate leakage where the aerial wire leads in the
station to the instruments is shown in Fig. 254 and is due to L)r.
Braun; it will be seen that the leading-in wire passes through a
porcelain bushing inserted in an aperture cut in the window-pane.
FORMS OF AERIALS. — The early Popoff antenna consisted of a
lightning-rod, while that employed by Marconi in his first essays
comprised a single copper wire leading from the instruments and to
a large metal plate which was attached to its upper free terminal
FIG. 255. — FORMS OF AERIALS.
as in Fig. 252. Various forms of aerial wires are shown in
Fig. 255; the object of adding to the number of wires
is to obtain a greater radiating and receptive surface; refer-
ring to the figures, a is the ordinary single wire aerial, b parallel
wires which are in some cases arranged in fan shape, c multiple
quadrangular aerial, d multiple cylindrical aerial, and e inverted
pyramidal aerial for long-distance transmission. The length of
aerials range from 50 to 200 feet. Fleming has pointed out that
if an aerial is composed of seven strands of wire, each having a
AERIAL WIRES AND EARTHS.
241
diameter of No. 22 B. S. G., and a length of 150 feet, and insulated
from the earth, its capacity, if held vertically, is 0.0003 micro-
farads. If a number of wires are placed very closely together,
their combined capacity is not nearly equal to the
sum of their individual capacities,1 and therefore
the wires should be placed at a considerable distance
apart.
LODGE CAPACITY AERIALS. — The earliest form of
aerial devised for the purpose of selective signaling
is due to Lodge, and is shown in diagram Fig. 256.
Two cones of large dimensions were made of metal
and insulated from each other and the earth. These
served to increase the capacity of the system as well
as to radiate and receive the electric waves. The
capacity areas were of definite value, but were con-
nected with an inductance coil, so that this factor
could be varied at will.
GUARINI SHEATHED AERIAL. — The fact that elec-
tric waves are intercepted, reflected, and absorbed by
metals led Guarini to devise the sheathed aerial shown
in Fig. 257 ; the aerial wires emitting and receiving
the waves were insulated and then encased in a me-
tallic sheath diverging at the top, forming a cylinder
of large diameter in which a slot was cut ; the purpose
of this arrangement was to reflect
the emitted waves in a given direc-
tion or to receive them from a given
point of the compass. There is a
very great loss of energy in this
method of transmission, but in spe-
cific cases it might be useful. When
receiving, all extraneous electric
waves are either reflected from the
sheath surrounding the aerial wire
or transformed into oscillations
which are conducted to the earth.
TOMMASI-JEGOU DIFFERENTIAL
WIRE AERIAL. — The differential
aerial system introduced by Tom- FIG. 25?.— GUARINI SHEATHED AERIAL.
'Cantor Lectures, Journal of the Society of Arts, London, March, 1903.
FIG. 256.
LODGE CAPAC-
ITY AERIAL..
242
WIRELESS TELEGRAPHY.
masi-Jegou some years ago was intended to receive various
wave lengths simultaneously by employing two or more wires
at the transmitting station A, Fig. 258; these radiating wires
were of different lengths. At the
receiving station B, 5 kilometers
distant, the antennas is equal in
length to the shorter one at A,
while at the Station C the an-
tennaa is equal to the longest wire
at A. By a proper adjustment the
indicators were not actuated except
when the shortest wire at A is send-
ing to B or the longest one at A to
C, except where a definite value of
the distance produces a neutral effect
on both receivers.
MARCONI AERIAL (SECOND FORM). — The aerials employed by
Marconi in his first syntonic system, composed of inner and outer
A BC
Fio. 258. — JEGOU DIFFERENTIAL
AERIAL.
— MARCONI CYLINDRICAL AERIAL.
metal cylinders, mark the first attempt to eliminate the high vertical
wire as a factor in wireless telegraphy. Marconi has used single
AERIAL WIRES AND EARTHS.
243
cylinders of four or five meters in height in some of his experiments,
and it is stated that messages have been sent and received a distance
of twenty miles with their aid. A wireless telegraph automobile
designed by this inventor for military purposes is equipped with an
adjustable cylinder arranged to fold back on top of the vehicle
when not in active service. It is illustrated in Fig. 259.
SLABY-ARCO DIRECT EARTHED AERIAL. — To • Dr. Slaby and
Count Arco is due the credit of having employed the sending and
receiving aerials directly connected with the earth. Before the re-
searches which led to this method it was the common practice to
connect the lower free end of the aerial
wire with one side of the spark-gap or
coherer and the earth to the comple-
mentary side, but it was subsequently
found that if the oscillators and wave
detectors were connected to the aerial
wire at a point where it formed contact
with the earth, as in Fig. 260, the po-
^EEF ~^ tential of the oscillations was equally
a effective, while the discharge of atmos-
FIG.' 260.-SLABY-ARco DIRECT Pheric electricity through the detector
EARTHED AERIAL. would be dissipated in the earth at A.
in accordance also with the theory evolved, all waves received by the
aerial which were not of a predetermined length will pass into
FIG. 261. — BRAUN NON-EARTHED
the earth, since the nodal point is at A ; the aerial wire should be
in this case one-fourth the length of the wave it is desired to re-
ceive.
BRAUN ARTIFICIAL EARTH. — In Braun's system the radiator,
Fig. 261, A, is connected with the primary of a transformer coil, a,
whose opposite terminal is not earthed, but is attached to a cylinder
244 WIRELESS TELEGRAPHY.
of copper or zinc, illustrated in the photographs, Fig. 262. This is
one of the striking features of the Braun system and an original
departure in commercial wireless telegraphy. It is claimed that
this method effectually eliminates the disturbances due to atmos-
pheric electricity. The aerial wire forming the antenna of the
resonator is divided by the condensers,, c, c, and the primary of the
transformer coil, T, as shown in Fig. 197.
DE FOREST MAST AND AERIAL. — One of the stations of the De
FIG. 262.— BRAUX ARTIFICIAL EARTHS.
Forest system is located at Steeplechase Park, Coney Island. It is
equipped with a mast 210 feet in height; it is constructed of four
poles set in crosstrees and supported by square bars of iron with a
shoulder at one end to sustain the topmast over the head of the
lower mast, and are termed fids; the mast is guyed to braces sunk
into the sand sixteen feet deep. The guys are of wire rope with
hemp rope terminals spliced in about 100 feet from the ground;
the object of this combination is to maintain the insulation of the
aerial cables, of which there are two supported by a yardarm near
the top, and prevent them from coming in contact with the guys.
It is illustrated in Fig. 263. A number of other masts, aerials and
AERIAL WIRES AND EARTHS.
245
stations are shown giving an excellent idea of the individual ar-
rangements. Fig. 264 is a Fessenden New York-Philadelphia, 135
foot aerial ; Fig. 265, a Marconi station at Rosslare, Ireland ; Figs.
266 and 267, are Slaby-Arco stations at Sapnitz and Gross Molen
FIG. 263. — DE FOREST MAST AND AERIAL.
respectively ; a Braun-Siemens and Halske equipment at Helgoland
is illustrated in Fig. 268, while Fig. 269 shows a French school-
ship with Branly-Popp aerials.
FESSENDEN WAVE CHUTE. — In a recent patent granted to Fes-
senden additional data are given relating to aerials and grounds.
This physicist has found it desirable to have a highly conducting
surface over which the waves are propagated in the neighborhood
of the point where they are generated, and that this highly conduct-
246
WIRELESS TELEGRAPHY.
ing surface should extend to a distance from the point of their pro-
duction at least one-fourth of the length of the wave in air and in
the direction toward the station to which it is desired to send the
message. The diagram, Fig. 270, illustrates the method for produc-
ing the desired results and is termed by Fessenden a wave chute;
in the figure, 1 is the sending conductor, and 2, 2', 2" is the
grounded conductor leading across buildings and other obstacles to
FIG. 264.— FESSENDEN MASTS AND STATION.
I beyond the limit of obstructions when the terminals are earthed
as shown. The coils 3, 3, 3, 3, forming guys from the mast, have a
period of oscillation different from that of the antenna, and this-
with the grounded conductor or wave chute eliminates the inter-
ference of extraneous waves and serves to dissipate atmospheric
potentials which occur in ordinary aerial wire systems. In practice
Fessenden employs a sending wire having a large capacity and low
inductance. The former is regulated by increasing the area of the
AERIAL WIRES AND EARTHS.
247
aerial wire and the latter by adding to the number of turns of wire
connecting the vertical wire with the oscillator.
KITE-SUSTAINED AERIALS.— With the advent of the auto-co-
herer and current-actuated detectors came portable transmitters and
receptors and the kite-sustained aerial wire. Heretofore one of the
greatest obstacles in the successful transmission of wireless messages
FIG. 205.— MARCONI MAST AND STATION.
in military operations was the heavy accouterments entailed by the
use of masts, as these are much too cumbersome to be transported
with the facility necessary in such all-important operations, and
instruments without 80- or 100-foot aerials are useless. The kite
and the balloon offer the solution. Kites are preferable, except in
cases when there is no wind, and then small hydrogen gas-bags are
useful. In the Branly-Popp wireless telegraph automobile ambu-
lances, balloons are employed. The exterior and interior of these
248
WIRELESS TELEGRAPHY.
ambulances are reproduced in Fig. 271. Various forms of kites
especially adapted to the velocity of the wind may be obtained
for elevating and sustaining the aerial wires. The aerial is
JIG. 266. — SLABY-ARCO MAST AND STATION.
attached to the kite as illustrated in Fig. 272. Aluminum wire,
in virtue of its extreme lightness, makes a desirable vertical wire
for this purpose. The transmitter and receptor utilize the same
AERIAL WIRES AND EARTHS. 249
vertical wire for radiating and receiving the waves, the change being
made by means of an ordinary switch.
In very light winds the Malay, or, as its improved form is known,
FIG. 267. — SLABY-ARCO AERIAL AND MAST.
the Eddy kite, is largely employed ; it is shown in Fig. 273. These
kites are fitted with a "bridle," which is already adjusted. To the
ring or loop at the center of this bridle the end of the ball of kite-
250
WIRELESS TELEGRAPHY.
cord is secured so that the knot is a firm one. These kites are tail-
less, may be flown in a very light breeze, and a number of the kites
may be connected in tandem and their sustaining properties in-
creased. In winds having a higher velocity the cellular or the
American modification of it, known as the Blue Hill box kite,
FIG. 268. — BRAUN-SIEMENS AND HALSKF. AKRIAI. AND SUPPORT.
shown in Fig. 274 in outline, and a photographic reproduction
in Fig. 275, may be used. It has a large sustaining surface and
may be used in winds of ordinary velocities; in winds having a
velocity of thirty or forty miles per hour a box kite having a very
small sustaining surface is especially serviceable, since it pos-
sesses marvelous stability. Fig. 276 is a complete portable army
AERIAL WIRES AND EARTHS.
251
equipment constructed by the Braun- Siemens and Halske Com-
pany for the German Government; it was placed in charge of
FIG. 269. — BRANLY-POPP EQUIPMENT ON SCHOOL SHIP.
FIG. 270. — FESSENDEN WAVE CHUTE.
the Royal Military Aerostat Battalion; Fig. 277 shows the aerial
wire suspended from a kite and the instruments in operation. The
transmitting apparatus includes a dynamo direct connected to a
252
WIRELESS TELEGRAPHY.
gasolene engine and is arranged on one gun carriage while the
receiver is placed on another.
MARCONI CABLELESS STATION AERIAL. — The first trans-Atlantic
signals transmitted from the cableless station at Poldhu, England,
FIG. 271. — BRANLY-POPP AUTOMOBILE AMBULANCES.
on December 12, 1901, were received by a single aerial wire sus-
pended from a kite at an elevation of 400 feet at St. John's,
Newfoundland; the kites employed during these aerial tests
FIG. 272. — KITE SUSTAINED AERIAL.
were constructed on the same general lines as those designed
by Major Baden-Powell, consisting of a bamboo frame nine feet in
height covered with silk and having a hexagonal form. The aerial
wire passed through a window and was attached to a pole, and from
AERIAL WIRES AND EARTHS.
253
this it led to the kite. The wire leading to earth forming the oppo-
site arm of the resonator was suspended over the cliff from the
station at Signal Hill and was connected to heavy plates of
FIG. 273.— EDDY KITE.
copper anchored in the sea. The aerial wires of the trans-
mitting station at Poldhu, England, consisted of 15 vertical wires
suspended from masts 210 feet in height and were arranged in a
FIG. 274.— BLUE HILL Box KITE.
circle. The construction of the multiplex aerials at Glace Bay,
Novia Scotia, and South Wellfleet, Mass., cableless stations are
designed especially for emitting long and powerful electric waves.
W7J? ELESS TELEGRAPHY.
J. 275. — STARTING THK Hox Kin.
FIG. 276. — BRAUN-SIEMENS AND HALSKE PORTABLE ARMY EQUIPMENT.
FIG. 277. — ARMY EQUIPMENT IN OPERATION.
AERIAL WIRES AND EARTHS.
255
FIG. 278. — MAKCONI SOUTH WELLFLEET TOWERS UNDER CONSTRUCTION.
FIG. 279. — SOUTH WELLFLEET TOWERS COMPLETED.
256
WIRELESS TELEGRAPHY.
FIG. 280.— MARCONI CABLELESS STATION.
FIG. 281.— THE "CARLO ALBERTA."
AERIAL WIRES AND EARTHS. 257
Figs. 278, 279 and 280 are photographs of the South Wellfleet sta-
tion in the course of construction; four wooden standards 210 feet
in height are arranged in a quadrangle and are sustained by guy
wires ; the aerial is composed of 400 wires forming an inverted pyra-
mid ; the upper terminals are insulated and the lower ends terminate
in a single conductor of large dimensions. The opposite arm of the
system is connected with several large metal plates deeply imbedded
in the earth to make good contact. For the purpose of testing the
range of wireless telegraphy over land and sea, the King of Italy
placed the magnificent man-of-war Carlo Alberto at Marconi's dis-
posal. It was on this vessel that the greatest achievements of this
brilliant young inventor were consummated when he kept in touch
with the Poldhu station, while in the Mediterranean and across the
Atlantic Ocean.
CHAPTER XVIII.
RESONANCE.
HISTORICAL.
Electrical resonance effects have long been observed in connec-
tion with low-frequency alternating currents. Lenz investigated
these current waves over fifty years ago1 and Koosen described the
exalting effects of a circuit having a certain capacity and inductance
in 18542; many years ago Siemens Brothers found that the volt-
age from an alternator was increased in a closed*circuit cable im-
mersed in a tank of water. This phenomenon, which may be termed
simple electrical resonance in accordance with its acoustic analogue,
is sometimes referred to, though improperly, as a Ferranti effect,
and was noted and carefully analyzed by Fleming in the con-
centric cables connecting London with Deptford3; and finally in
1894 Pupin evolved a complete theory of alternating-current res-
onance which he set forth in a paper read before the American
Institute of Electrical Engineers.4 In 1885 Overbeck determined
that a large value of inductance resulted in a circuit having the
same period of oscillation,5 and in 1887 Hertz obtained sym-
pathetic resonance phenomena between mutually reacting circuits ;6
Hertz plotted resonance curves and Bjerknes obtained similar re-
sults and verified the correctness of these curves by experimental
measurements in 1891,7 and finally Lodge devised his syntonic
Leyden jars which required a fine adjustment of their coefficients
to effect sympathetic resonance and upon which the whole scheme
of syntonization of wireless telegraph apparatus has been founded.8
^Poggendorfs Annalen, vol. 76, 1849.
*Poggendorfs Annalen, vol. 92, 1854.
^Journal of the Institution of Elec. Engs., vol. 20, p. 362.
'Transactions Institute of Elec. Engs., New York, 1894.
•Of. Overbeck. Weidemann's Annalen, vol. 26, p. 245, 1885.
6Hertz, Weidemann's Annalen, vol. 31, p. 421, 1887,
7N. Bjerknes, Weidemann's Annalen, vol. 44, p. 74, 1891.
*Nature, Vol. 40, p. 368.
258
RESONANCE.
259
THEORETICAL.
Electric resonance phenomena are strikingly similar to those of
acoustic resonance. Electric resonance, like its acoustic analogue,
may be simple or sympathetic ; in sound, simple resonance is a direct
reinforcement of a simple vibration, and may be demonstrated by
whistling at a low pitch across the open mouth of a bottle and then
raising the pitch until a corresponding frequency of vibration equal
to that of the natural period of the bottle is reached, when the latter
FK;. 282. — SIMPLE; ACOUSTIC KUSONA:
will emit a similar sound and reinforce the note in strength and
quality1 (see Fig. 282). In simple electric resonance an alternating
current of high or low frequency flowing through a circuit having
inductance and capacity, if the frequency of the alternation or
oscillation is proper, will surge through the circuit and its voltage
will be augmented by resonance until it may be at least four times
1 Architectural Acoustics. Kelly.
260 WIRELESS TELEGRAPHY.
greater than its normal value, or, expressed symbolically, if the
frequency of the current is N and the capacity of the circuit is C in
microfarads and the inductance of the circuit is L in henries, then
resonance will take place when
!/ 2irCL
The degree of resonance is limited largely by the resisting properties
of the circuit and losses due to the imperfect elasticity of the
medium. Thus the higher the frequency of the current, the
smaller becomes the effect of resistance in the circuit and the more
nearly is pure resonance approached. Primary resonance in an
ordinary open-circuit oscillator system has been likened by Fleming
to that of acoustic resonance in a closed organ-pipe ; thus the radiat-
ing aerial wire when its current is oscillating with a frequency
natural to its dimensions corresponds to the fundamental frequency
of an organ-pipe, and the similarity does not end here, for the radi-
ating aerial wire has a very low potential difference and a large
current strength at its spark-gap terminal, representing a crest of
the current wave and a node of potential, while at the upper and
free end of the aerial radiating wire there is a reverse condition of
affairs, for here the potential difference is maximum, forming a
loop, and the current is now minimum, forming a node, just as
there is a very slight difference in the oscillation of the air molecules
or pressure and a great alternation of air movement at the mouth
of the organ-pipe, while at the upper end of the pipe there is a
great variation of the air molecules and a corresponding increase in
air movement.
If air at a certain* pressure is admitted to an organ-pipe of
proper dimensions a primary note will be emitted that is called the
fundamental; likewise when the primary oscillations of an electric
current correspond to the dimensions or natural period of a circuit,
waves having a fundamental frequency will be emitted. By vary-
ing the pressure of air in an organ-pipe the fundamental note may
be substituted and tones of different values will be produced1, which
are the harmonics of the fundamental, and so also by impressing
upon a radiator or resonator system a current of predetermined
frequency, harmonic oscillations will be set up and the waves they
emit find their analogue in the overtones of an organ-pipe.
aThis fact was discovered by Daniel Bernoulli!, a mathematician.
RESONANCE.
261
EXPERIMENTAL.
The loops and nodes of electric oscillations may be exhibited in a
very striking manner by an apparatus devised by Dr. Seibt.1 It
comprises an induction coil, 1, Fig. 283, the secondary terminals con-
necting with the spark-gap, s; the oscillator system includes the
FIG. 283. — SEIBT SIMPLE ELECTRIC RESONANCE APPARATUS.
spark-gap, one terminal of which leads to a variable inductance, L ;
the opposite terminal connects with the outer coating of a Leyden
jar, C, and to earth at e ; the jar, C, is in series with a second jar, C1,
the inner coating of which connects with the inductance, L, forming
a closed circuit; from the inductance, L, there extends vertically
a spiral of silk insulated copper wire six feet in length by two
inches in diameter supported on a wooden core; parallel with the
closely wound spiral of wire is a straight copper wire, E9 grounded
at e. If now the apparatus is placed in a dark room and oscillations
are impressed on the spiral wire having a frequency corresponding
to the natural period of the circuit, a luminous glow will be ob-
served to take place between the spiral and its complementary
'Cantor Lecture, Society of Arts, London, March, 1903.
262 WIRELESS TELEGRAPHY.
straight wire showing visually the difference of potential represented
by the wires ; and if the oscillators are tuned to the natural period of
the circuits, the glow will increase gradually from the bottom to the
extreme ends of the wires, where it will be maximum. But if the
values or the coefficients are rearranged by varying the inductance
and capacity so that the frequency of the oscillations may be in-
creased, a node will be formed at A, or one-third of the length of the
coiled wire from the top, and the glow or brush discharge will be
minimized, shown by the dotted line, indicating that the first
harmonic of the fundamental has been reached; by decreasing the
capacity and inductance of the circuit the second overtone or
harmonic may be produced and observed.
SYMPATHETIC KESONANCE. — In acoustics, sympathetic resonance
is the vibration of any musical tone in response to a musical tone
Flo. 284. — HBRTZ SYMPATHETIC RESONANCE APPARATUS.
of the same pitch ; as an illustration, let a note from a trombone be
emitted in front of a pipe organ, when the pipe, having a similar
period of vibration, will respond in virtue of their natural periods
being equal. Sympathetic electric resonance is the tuning of two
circuits so that an oscillating current set up in the first will start
a train of high-frequency oscillations of exactly the same period in
the second circuit. One of the fundamental laws upon which elec-
tric resonance is based is that an oscillating current of definite
frequency will set up a greater potential difference in a resonator
tuned to the same frequency of oscillation than in one whose natural
period of oscillation is different. Hertz produced sympathetic
electric resonance by means of the simple apparatus shown in Fig.
284. The oscillator B C C' is charged to a sparking potential by the
induction coil ; A, the resonator, abed, was formed of wire ending
in small spheres and separated a distance of a tenth of a milli-
RESONANCE.
263
meter. An open-circuit resonator, Fig. 285, was substituted by
Hertz for the rectangular closed-circuit resonator just described,
and by adjusting the capacity and inductance to a suitable value
resonance was obtained as before.
For obtaining the highest degree of resonance between two
mutual circuits the oscillator and resonator should be closed, since
it has been shown that high-frequency currents are not damped out
as rapidly in closed circuits as in open circuits, and therefore the
D
D
n
FIG. 285. — OPEN-CIRCUIT RESONANCE APPARATUS.
waves emitted approach more nearly a sinusoidal curve, which is
extremely desirable; but, conversely, a train of electric waves from
a closed-circuit oscillator has not the powerful and penetrating
qualities of waves emitted by the quickly damped oscillations of an
open circuit. A closed-circuit apparatus devised by Lodge to illus-
trate sympathetic resonance is shown in Fig. 286 ; the radiator con-
sists of a Leyden jar, a, connected with an induction coil, I ; the
FIG. 286. — LODGE SYNTONIC JARS.
inner and outer coatings of the jar are connected with a loop of
wire a meter in diameter and separated by a spark-gap, c; the
resonator has a Leyden jar, d, of equal capacity arranged with an
overflow path having a minute air-gap forming the detector; the
coatings of the jar are connected by a loop of wire of similar di-
mensions to those of the radiator, but the closure is made by a wire
sliding over the terminals of the loop ; now if the first jar is dis-
charged, the second jar, if it is in tune with it, will discharge across
the air-gap detector, e ; the wire slide, /, serves to tune the resonator
with the oscillator by varying its value of inductance; in this sys-
2f)4
WIRELESS TELEGRAPHY.
tern thirty or forty oscillations surge through the circuits on the
discharge of radiator circuit.
DETERMINATION OF PERIODICITY. — To determine the periodicity
of oscillations occurring in the phenomena of resonance Bjerknes
FIG. 287. — RESONANT OSCILLATIONS
plotted the curves in Figs. 287 and 288, showing graphically
syntonic values. The oscillations of an open-circuit radiator or res-
onator are rapidly damped out, as before stated, in virtue of their
transformation into free electric waves; but in a closed-circuit
resonator high-frequency currents will continue to oscillate for a
FIG. 288. — PHASE DIFFERENCE OF ELECTRIC OSCILLATION.
considerable time after the co-resonant oscillator has ceased to emit
waves. Fig. 287 is a curve showing graphically the amplification of
oscillations in a closed-circuit resonator such as Hertz used as a de-
tector after excitation with an oscillator in syntony with it ; in this
case the circuits were accurately syntonized with the oscillator, as
the increasing amplitude of the swings plainly indicate. In a
closed-circuit resonator that is not quite in tune with the oscillator
emitting the waves the curve shows the 'varying difference in phase
by the greater and lesser amplitudes. Where the resonator is com-
pletely out of syntony with the oscillator then a counter-action takes
place, and however close the oscillator may be to the resonator, there
will be no currents set up in it, for each succeeding impinging
RESONANCE. 205
wave damps out the feeble impulse of the preceding one, since they
are not properly tuned to the coefficients of the circuit.
APPARATUS FOR PLOTTING RESONANCE CURVES. — The resonance
curves referred to were plotted by Bjerknes by means of an open-
circuit Hertz oscillator, 1, Fig. xi8(J, a closed-circuit resonator, 2, and
a one-sided electromotor. 3 ; the electrometer was attached to the
resonator so that the quadrants of the former were included in tho
circuit of the latter as shown in Fig. 139 ; when no current is surg-
ing in the resonator system the double quadrants equally attract
the needle when it rests at zero potential; but when high-frequency
oscillations traverse the circuit the needle is deflected to the right
FIG. 289. — BJEKKNKB HKSONANCK APPARATUS
and the left, making it easy to determine with considerable accuracy
the damping coefficients of the circuit1.
RELATION OF COEFFICIENTS TO RESONANCE. — The laws under-
lying sympathetic resonance involve, as they do in primary reson-
ance, the coefficients of capacity, inductance, and resistance, but
in this case deal with two mutual circuits. Starting with a
capacity and inductance of a given value in the oscillator and
resonator systems when resonance obtains, it has been mathemat-
ically ascertained and experimentally determined that syntoniza-
tion remains unaffected if these factors are changed equally in
both circuits; again, either the capacity or inductance may be in-
creased or decreased individually in the oscillator without materially
altering the resonance effect, provided that like values of the co-
efficients of the resonator shall be made equal or that the coefficients
of the resonator shall represent some multiple or sub-multiple of
the oscillator system; the resistance at all times of both circuits
should be as low as possible, and for this reason a current-operated
detector is preferable to a voltage-operated detector. There are
exceptions to the above rule, as, for instance, where the capacity of
decrement of Electric Oscillations. M. V. Bjerknes, Comptea Rendus,
June 22, 1871.
266
WIRELESS TELEGRAPHY.
a circuit may be decreased by increasing its inductance without de-
stroying the resonance qualities; this is due to the fact that the
harmonics of the circuit are based upon the product of its capacity
and inductance.
Exceeding care must be exercised in tuning and syntonizing
electric circuits for the production of resonance phenomena, and
FIG. 290.— HOT-WIRE AMMETER.
the desired results may be much more easily obtained by the varia-
tion of capacity than by changing the values of inductance. When
resonance is effected a very slight addition or reduction of capacity
will be sufficient to throw the co-resonant circuits out of syntony
RESONANCE.
267
and effectually prevent the resonator from responding to 'the oscil-
lator.
TUNING CLOSED TO OPEN OSCILLATOR CIRCUITS. — The method
usually employed in practice in tuning a closed oscillator cir-
cuit to the aerial or open oscillator system is by means of a hot-
wire ammeter. Assuming the apparatus to be of the compound
circuit type and that the connections have been properly made, a
hot-wire ammeter, shown in Fig. 290, is inserted in circuit with
the shunt and aerial wire indicated in the diagram, Fig. 291. The
sliding contacts 1 and 2 rest on an inductance coil and these are first
brought together to cut out the inductance. The primary circuit is
then closed by depressing the Morse key while the contacts are
gradually separated until the ammeter gives the highest reading.
FIG. 291. — TUNING OSCILLATOR CiRcurrs.
When this is determined the speed of the interrupter tnfcy be vai led,
since a higher reading may sometimes be had by a careful adjust-
ment of the make and break device. Occasionally the final position
of the sliding contacts may result in an overtone or minor wave
length. In the Slaby-Arco transmitters installed on vessels in the
United States Navy the wave length used is about 200 meters, which
is the length produced by a closed circuit consisting of seven Leyd^n
jars and approximately qne turn of inductance.
TUNING RESONATOR CIRCUITS. — With every syntonized receptor
system there should be supplied an inductance coil for tuning the*
open and closed circuits similar to that employed in the oscillator
systems. The tuning, however, is accomplished by more or less arbi^
trary methods. Since the capacity of the coherer is varying con-
stantly, the sliding contacts can only be approximately adjusted
268 WIRELESS TELEGRAPHY.
Then when possible to receive from some transmitter whose wave
length is normally that desired to receive by, the operator of the
former should transmit a test letter repeatedly at short intervals of
time, gradually decreasing the amount of energy, while the operator
at the receiving station should adjust his tuning coil until the letter
is received to the best advantage, when the relative values of the
open and closed circuits and the resonator and oscillator systems will
be co-resonant. The aerial wire of the resonator should as nearly
equal the length of the oscillator aerial as possible, in order that
sharp resonance may obtain.
KESONANCE IN WIRELESS TELEGRAPHY. — The efforts to employ
electric resonance in wireless telegraph apparatus so that a trans-
mitter, tuned to a definite period of oscillation and sending out in
consequence waves of predetermined lengths only, would set up
oscillations in a receptor whose resonator system was tuned to a
similar frequency, and therefore in syntony with the oscillator, has
called forth many ingenious and striking combinations. Since per-
sistent oscillations are essential to a syntonic system of precision, it
is evident that closed circuits are eminently adapted for sympathetic
resonance effects, but it has also been pointed out that such closed
circuits are exceedingly poor radiators, and therefore quite un-
suitable for long-distance wireless transmission ; oppositely disposed
is the fact that while open-circuit systems emit powerful waves,,
their damping coefficient is so large that their application to syn-
tonic wireless telegraphy is very limited. These untoward condi-
tions, together with that offered by the unknown factors the earth
presents, are problems on which much time and thought have been
expended. To overcome these objectionable features many combi-
nations of open and closed circuit systems have been devised in
which persistent oscillations would be set up in a closed circuit of
an oscillator first, and by transformation be made to oscillate in an
open circuit, where they are damped out successively by conversion
into electric waves instead of radiating all their energy in two or
three swings; a resonator designed on similar lines to those em-
bodied in its complementary circuit radiating the waves is so ar-
ranged that the emitted waves impinge on an open-circuit resonator
first, and are then transformed into oscillations in a closed cir-
cuit, where they surge to and fro many times before their energy
is absorbed bv the total resistance of the circuit.
CHAPTER XIX.
SYNTONIZATION.
HISTORICAL.
Recognizing the vast importance of a syntonic system of wire-
less telegraphy whereby a plurality of oscillators and resonators in
the same field of force may selectively communicate with any in-
dividual station to the exclusion of all others, Lodge' invented and
patented an apparatus in England in 1897,1 involving the prin-
ciples of electrical resonance. This was an open-circuit sys-
tem having a high time constant, and therefore utilizing long
electric waves. The value of closed-circuit systems in resonance
phenomena and of open-circuit systems for long-distance trans-
mission now called forth the best efforts of the workers to effect
a harmonious combination in which the desirable qualities of both
should be retained. Slaby and Arco of Germany devised a system
for this purpose in 1898-99, and described it in detail in 1900. 2
Simultaneously Marconi was working out the principles of a syn-
tonic system by which the persistent oscillations in a closed cir-
cuit could be utilized, the high aerial wire eliminated, and the
for this purpose in 1898-99, and described it in detail in 1900.2
In the same year Braun evolved a system of selectivity based on
the proper proportioning of the coefficients of both open and closed
circuits, and, reversing the methods above cited, he eliminated the
earth and retained the antenna.4 In 1902 Fessenden devised aii
electro-mechanical multiplexing system, the transmitter having
acoustic tuning-forks with make and break mechanism adjusted to a
certain number of vibrations and the receiver having electro-mag-
nets or telephones with armatures or tongues vibrating at a period
British Patent, Lodge, 11,575, 1897.
2Syntonized and Multiplex Spark Telegraphy. General Elec. Co., Dec.
22, 1900.
'Progress of Electric Space Telegraphy. Royal Institution, June 13,
1902.
*Elec. World and Eng. Braun, Siemens & Halske System. Collins, June
14, 1902.
260
270 WIRELESS TELEGRAPHY.
equal to those of the transmitting forks.1 A selective system has
been produced by Mr. John Stone Stone,2 of Boston, in which two
simple circuits are associated inductively, each having an independ-
ent degree of freedom, and in which the restoration of electric oscil-
lations to zero potential the currents are superimposed, giving
rise to compound harmonic currents which permit the resonator
system to be syntonized with precision to the oscillator.
A patent issued to Nikola Tesla on March 17, 1903, for a
syntonic system of wireless telegraphy describes an apparatus em-
ploying two oscillators at the transmitting station, each having
its own aerial wire; a single key operates both simultaneously.
At the receiving station there are two resonators syntonized to the
individual frequencies of the oscillators, and when the circuits
are syntonic the relay of the receptor is acted upon, but if one
of the circuits is not in accord with the other no signal will re-
sult.
A strictly mechanical system of selective wireless telegraphy
in which electric resonance is eliminated as a factor has been de-
vised by Anders Bull,3 of Christiania, Norway. The mechanism
is operated electrically. By this system three wireless messages
have been sent and received simultaneously and selectively, being
the first time in the art that mechanical methods have been em-
ployed successfully in obtaining selectivity.
PRACTICAL.
Selective wireless telegraphy has been developed along three
distinct lines, i.e., electrical, electro-mechanical, and mechanical.
In the electrical method the principles of resonance are called into
practice; in the electro-mechanical method, tuned circuits are
combined with mechanical vibrators, and in mechanical methods
mechanism is actuated by impulses from the transmitter operating
synchronously with the receiver.
LODGE TUNED SYSTEM. — In the Lodge tuned system of wireless
telegraphy, shown in Fig. 293, the method of selective intercommu-
nication consists of producing and detecting a sufficiently prolonged
series of rapid electric oscillations so arranged that a particular
'Letters Patent. Fessenden, 715,203, Dec. 2, 1902.
2 Letters Patent. Stone, 714,756.
3 Electrician, London, 1903. Experiments on Selective Wireless Teleg-
raphy. Anders Bull. Oct. 2.
SYNTONIZATION.
271
frequency of oscillation at the sending station may cause an instru-
ment to respond at a distant station tuned to some multiple of that
FIG. 293.— LODGE TUNED SYSTEM.
a c
FIG. 294. — SLABY-ARCO MULTIPLE SYSTEM.
frequency. The inductance coil of the radiator, A, Fig. 293, pro-
longs the oscillations, so that the emitted waves have a definite
272 WIRELESS TELEGRAPHY.
period. The resonator, B, Fig. 293, having the same electrical
dimensions as the radiator, the number of oscillations set up in
the former is very large, for the feeble impulses are gradually
strengthened by cumulative action until the resistance of the wave
detector is broken down. A complete set of Lodge's apparatus was
shown in operation at the Royal Society Conversazione in London,
May 11, 1898, and operated in a manner most satisfactory.
SLABY-ARCO MULTIPLE SYSTEM. — The principles upon which
the Slaby-Arco multiple wireless telegraph system is based will be
readily understood by referring to the diagram, Fig. 294, where
A and B represent the aerial wires at a distance from each other ;
when oscillations are set up in A of a definite frequency syntonic
oscillations will surge through J5, the amplitude of which will fol-
low a sine wave law between the free terminals, a, c, and the earthed
terminals, b, d, the* amplitude being greatest at a, c, that is, if
the aerial wires are each one-fourth of the wave in length, when
the earthed terminals will form the nodal point of the oscillations.
Postulating that such is the case, then it is evident that, since the
point of greatest amplitude of the an-
j tenna is at c, B, the wave detector,.
should be placed so that this maximum
potential difference may be impressed
I upon it. But it is not necessary for the
i coherer to be placed at the free terminal
/ of the receiving antenna, for the same
effect is obtainable by connecting a hori-
^^- ----- I zontal wire with the vertical air wire at
-^--.^ " its nodal point, i.e., the earth, and
FIG. 2M.-Porl^ LOO™ ANB then connecting the free terminal
NODES. of the horizontal wire to a co-
herer as shown in Fig. 295, when the amplitude of oscilla-
tion at & will be exactly the same as at a. In practice the
coherer is earthed where the oscillation again forms the nodal
point of the current wave. The damping coefficient of such an
oscillator and resonator is much less than in open-circuit systems,
and for this reason the persistency of oscillation is much greater
than it would otherwise be, although the aerial wires act as an
open-circuit radiator and resonator. The Slaby-Arco system was
exhibited before the German Emperor, and two messages, sent from
two different stations, were received simultaneously.
SYNTONIZATION.
273
MARCONI SYNTONIC SYSTEM (FIRST FORM). — In Marconi's
syntonic wireless telegraph system, shown diagrammatically in Fig.
296, the inventor has designed an oscillator in which high-frequency,
high-potential currents are not so powerful as in open-circuit oscil-
lators, but it emits long trains of waves instead of strongly damped
ones; a syntonic receiver will not respond to the first few feeble
FIG. 296. — MARCONI SYNTONIC SYSTEM.
wave impulses, but the cumulative effect of the train of waves
finally breaks down the resistance of the coherer when the indica-
tions take place.
FIG. 297. — MARCONI SYNTONIC SYSTEM. (Second Form.)
In this syntonic system Marconi succeeded in obtaining excellent
results with zinc cylinders 7 m. high and 1.5 m. in diameter be-
274 WIRELESS TELEGRAPHY.
tween St. Catherine's Point, Isle of Wight, and Poole, 30 miles
distant, the signals not being interfered with or deciphered by other
stations working in the immediate vicinity.
MARCONI SYNTONIC SYSTEM (SECOND FORM). — In his second
form of syntonic apparatus Marconi utilized an open-circuit oscil-
lator formed of the regulation aerial wires and earthed terminals.
The frequency of oscillation of the open-circuit radiator can be
regulated by increasing or decreasing the number of turns of wire
or by placing a variable' condenser in series with it, as shown in Fig.
297. The resonator of the receiver, B, is similar to that of the
oscillator, but leads to the earth through the primary winding of
the transformer, the secondary of which is connected to the wave
detector, To obtain resonance the open-circuit oscillator must have
FIG. 298. — MAP OP MARCONI STATIONS.
the same values of inductance and capacity as the open-circuit
resonator, which includes the primary winding and the condenser
referred to. This system was installed by the English Admiralty
between Portland and Plymouth, a distance of 65 miles as the bird
flies, and with hills 800 feet high intervening. At Poole and Niton
are Marconi stations likewise equipped with this type of syntonic
system, the distance being 30 miles. The lines of propagation of
these two systems cross each other at the angle shown in the map,
Fig. 298, and it was found that when both systems were tuned to a
different frequency messages could be sent simultaneously and ab-
solutely independent of each other.
BRAUN RESONANCE SYSTEM. — The arrangement employed by
Braun to obtain the maximum number of oscillations per charge
with the radiation of the greatest amount of energy per oscil-
lation and its complementary resonator, which is to a certain
extent its counterpart, is shown diagrammatically in Fig. 299. In
action it operates as follows: the oscillations set up in the closed
SYNTONIZATION.
275
circuit are impressed upon the open circuit by the linking of the
magnetic lines of force in the transformer coils, when the second-
ary receives the maximum potential of the high-frequency current
which are emitted from the open circuit; the impinging waves on
the antenna of the resonator are diametrically
opposite to that of the oscillator in that the
oscillations are set up in the open circuit first
and by conversion are made to surge in the
closed circuit, where they are not only persist-
ent, but by simple resonance are amplified in
potential until the coherer gives way and the
indication results. Braun's system has been
tested between Cuxhaven, Germany, and Heli-
goland, in the German Ocean, 36 miles distant,
with excellent success.
FESSENDEN SELECTIVE SYSTEM. — In addi-
tion to and in combination with the tuning de-
vices employed by Fessenden in his transmitter
and receiver, based upon the coefficients of the
oscillator and resonator, the electro-mechanical
apparatus shown diagrammatically in Fig.
300, forms a method of obtaining selective
signals independent of the dimensions of the
sending and receiving circuits; in the trans-
mitter the radiator, 1, is grounded through the
spark-gap, 2, in the usual manner. The pri-
mary of the coil is connected in series with the
battery, 4, and with two make and break
mechanisms, A, B, operated independently and
at predetermined but given rates of speed. The make and break
consists of a cup, 5, containing mercury, with a reciprocating pin, 6,
alternately making and breaking contact similarly to a mercurial
interruptor of this type, the motor, 7, serving to operate it.
The tuning forks, 8, 8, A, are adjusted to a given period and
correspond to the motor driven interruptor, 5, 6, 7, A ; likewise the
forks, 8, 8, B, have a period of vibration corresponding to the motor
interruptors, 5, 6, 7, B, but the A forks are tuned to a different
pitch from the B forks, e.g., A may be adjusted to 256 vibrations
per second while B may have 384 vibrations per second. The re-
ceiver is operated by the Fessenden detector, 11, connected in series
FIG. 299. — BRAUN RESO-
NANCE SYSTEM.
276
WIRELESS TELEGRAPHY.
with the antenna and ground; the local circuits, including two or
more electro-magnetic mechanisms operating in unison, have the
same periods of vibration as those of the transmitter. When a
message is sent the key 9 is depressed to make a dot or dash, and
during this time the make and break mechanisms send out groups
of electric waves, but one of the sets of groups emits waves at the
rate of 256 per second and the other at the rate of 384 per second,
and these different groups of waves acting on the resonator circuit
cause the tongues, 13, of the receiving mechanism to respond syn-
tonically and actuate telephone receivers. Fessenden has very re-
cently dispatched messages between Jersey City and Philadelphia,
FIG. 300. — FESSENDEN SELECTIVE SYSTEM.
a distance of 90 miles, and nearly all overland, with a minimum
of energy.
TESLA DUPLEX SYSTEM. — To eliminate the difficulty of resona-
tors responding to the upper and lower harmonies of other sys-
tems in the effective zone, Tesla has designed a duplex apparatus,
which he compares to a combination lock; two frequencies are
employed at both the sending and receiving stations, and when
these act in unison operate a common relay. This is accomplished
by generating two sets of oscillations, having different periods
surging in independent oscillators and receiving them by means
of independent resonators each of which is tuned to its comple-
OF THE
UNIVERSITY
OF
SYNTONIZATION.
277
mentary oscillators; AB, Fig. 301, represents diagrammatically the
sending and receiving systems. The radiators, D1, D2, are connected
to the terminals of the secondaries of two transformers, S1, S2, the
opposite terminals leading to earth, E, as in other systems. The
primaries, P1, P2, are in series with the inductances, L1, L2, and
the condensers, C1, C2', the condensers are energized by the gen-
erator, S ; shunted across the condensers is the spark-gap, D,
consisting of a rotating disk having projections, p, p, as shown,
which makes and breaks the disruptive discharge between the
electrodes, n, n, inserted in the holders, B1, B2. This discharge
disk is connected with the primary circuit at F and may also be
led to earth at E, when two independent primary circuits are
formed.
The duplex oscillators sending out energy in two different wave
lengths are impressed upon the resonators, e s1 d1 and e s2 d2,
I
FIG. 301. — TESLA DUPLEX SYSTEM.
syntonized to the sending station so that each responds exclusively
to one of the two frequencies at the transmitting station ; the elec-
tric wave detectors, a1, a2, are placed in the oscillator circuit leading
to earth at e; R1, R2 are relays in independent circuits actuated by
the resonators, and when these relays operate simultaneously the
internal circuit containing a third relay, R?, is closed; when the
relay R3 becomes operative it actuates the recording mechanism.
This system is said to work very well in the laboratory.
STONE MULTIPLEX SYSTEM. — The invention of Stone for mul-
tiplex selective signaling consists of a single vertical wire at the
transmitting station radiating electric waves of a single given
frequency. The oscillator is of the open-circuit type and is im-
278
WIRELESS TELEGRAPHY.
pressed with forced oscillations of a simple harmonic character
by means of a series of closed-circuit oscillators acting through the
medium of transformers. The receiver is made to respond to the
selective frequency of the oscillator by employing a periodic open-
circuit resonator and interposing between it and the translating
device a series of closed circuit resonators capable of responding
to a given and predetermined frequency.
In Fig. 302, A and B represent the transmitter and receiver
respectively. In these diagrams V is the aerial wires connected with
the earth, E, through the medium of the primary of a transformer,
I2, thus forming an open-circuit oscillator and resonator. The
secondary, I1 A, forms a closed-circuit oscillator, which includes
the inductance, L, condenser, 0, and spark-gap, 8', the local low-
frequency, high-potential circuit feeding the spark-gap is composed
FIG. 302. — STONE MULTIPLEX SYSTEM.
of the secondary of a transformer, I1,,, and the condenser, (7; the
primary local circuit consists of the inductor of the transformer, 112,
the key, K, and an alternating current generator, a. The receiver,
By is a physical counterpart of the transmitter in that its resonator
is of the open-circuit type and has combined with it a closed-circuit
resonator having a definite period due to the condenser, C1, and the
inductance, L\ the local circuit includes the coherer, E, the usual
battery, B, and the relay, R.
In action the condenser, C, discharges through the closed-circuit
resonator, Sl, L, and is of high frequency. The oscillations of this
circuit are simple harmonic in character and are unaffected by the
inductive association of the open-circuit oscillator because the in-
ductance of the closed-circuit resonator is large when compared with
that of the open-circuit oscillator. Now when two oscillators are
SYNTONIZATION.
279
inductively associated each has its own degree of freedom, or its
natural period of oscillation, and each is modified by the other, as
shown in the cuve, Fig. 303 ; but if the coefficients of each circuit
FIG. 303. — MODIFIED PERIOD OF OSCILLATION.
are such that the combined inductance of the two oscillators is large
when compared with the mutual inductance between the circuits,
Fio.. 304. — BULL SYNCHRONIZED SYSTEM. THE DISPERSER.
the natural period of oscillation becomes practically the same as if
the circuits were isolated. The object of this arrangement is to
obtain as nearly as possible a pure, simple, harmonic wave and to
280 WIRELESS TELEGRAPHY.
reduce to a minimum the minute overtones which cause a departure
from the true sine wave. At his stations on the Charles Eiver em-
bankment (Boston), Stone has shown it possible to transmit and
receive selective signals when the difference in frequency was not
more than ten per cent.
BULL SYNCHRONIZED SYSTEM. — A selective system of wireless
telegraphy based on mechanical principles has been invented by
Anders Bull. The apparatus comprises a transmitter and a receiver ;
the transmitter includes an open-circuit oscillator supplied with
energy by the usual transformer or induction coil operating through
FIG. 305. — BULL SYNCHRONIZKD SYSTEM.
tin Apparatus termed a disperse?', likewise the receiver has an
open-circuit resonator actuating a number of registers through a
mechanism termed a collector. The disperser is shown diagrammat-
ically in Fig. 304, and in half-tone in Fig. 305. By referring to
these figures it will be observed that the disperser, A, is connected
by gearing to the motor, B, a Siemens and Halske regulator, C, con-
trolling its speed. D is an electro-magnet automatically controlling
a disk, making a specific number of contacts and sending out a
similar and predetermined number of series of electric waves.
When it is desired to send a message, the key, I1, is depressed
and closes the circuit including the battery and electro-magnet, 2,
which attracts an armature attached to a clutch carrying a pin as
shown. The function of the armature, magnet, and clutch is
SYNTONIZA TION.
281
shown more clearly in Fig. 306, being a sectional view of the dis-
perser. When the armature is drawn to the magnet, 2, the disk, 3,
is released by the clutch, 4, and then revolves at a speed of about
5 r. per second. At every revolution of the disk, contact is made by
the springs, 6, and the circuit, including the battery, 7, and the
electro-magnet, 8, is closed. The disperser proper consists of 400
steel springs, 9, attached at right angles to the disk and near
its periphery; these long, vertical springs have their ends free
and pass through slots in a stationary and upper disk, 10; the
springs are thus permitted to move in a radial direction only;
a ring of brass forming a groove, 11, is fastened to the framework
and guides the springs so that with each revolution of the disk,
which is once every second, they either slide in the groove, 12, or
within its inner circumference. The bronze arc, 13, takes the place
FIG. 306.— DETAIL or TRANSMITTER.
of a section of the brass ring, 11, and has a finger projecting toward
the center of the disk; as the vertical steel springs come in con-
tact with it, they are forced toward the magnet, 14. Attracted by
this magnet, the springs slide along until released at the edge of
15, where they are again drawn into the groove or return to the
inner part of the ring by their own elasticity according to whether
the magnet is or is not energized.
Now in action when it is desired to send a dot the key is de-
pressed for less than a fifth of a second, or the time required for the
disk 3 to complete one cycle, and the current flows through the
circuit as a single impulse. When a dash is transmitted the key
is held in contact until the disk 3 has revolved a number of times,
when a corresponding number of electric impulses at one-fifth
second intervals flows through the circuit causing the springs to
make contact at regular intervals by means of contact points, 18,
282
WIRELESS TELEGRAPHY.
and thus closing the circuit in which the battery, 19, and the coil,
20, form a part. As there are a number of these contact points
arranged around the frame at prescribed distances, it is evident that
the number of series of electric waves emitted will be equal to the
number of contact points, and by varying the distance between these
points any combination or series of waves may be sent out through
the medium of the electro-magnetic key, 20, battery, 21, induction
coil, 22, and the oscillator circuit 23.
The collector is similar to the disperser except that receptive
devices are employed instead of emitting appliances in the circuits.
Tig. 307 is a plan view and 308 a half-tone of the collector. The
i :c. 307. — BULL SYNCHRONIZED SYSTEM. THE COLLECTOR.
coherer is connected in the open-circuit resonator in the usual man-
ner while the relay, 23, in series with a cell is included in a local cir-
cuit with the coherer. The tapper, 24, is in parallel with an auxil-
iary circuit formed by the armature of the relay in series with the
magnet, 25. For every series of electric waves that impinge upon the
resonator system one of the vertical steel springs slides into the
groove, 26, of the ring. The revolving disks of the disperser and col-
lector revolve synchronously, so that the angular distances of the
springs sliding in the grooves will be proportional to the time con-
stant between the series of the waves impinging on the vertical wire.
SYNTONIZA TION.
283
Since the points are arranged in the same relative positions in both
the disperser and collector, and are operated synchronously, contact
in both is made simultaneously. The points, 27, are connected in
series with the Morse printing register, 28. Now a prearranged
series of electric waves will cause the springs to make contact at
the same instant when the local collector battery operates the
Fio. 308. — BULL SYNCHRONIZED SYSTEM. THE COLLECTORS.
register. Electric wave series in succession will produce a dash or
a series of dots representing a dash.
In Bull's experiments one disperser and one collector were
employed, but these were arranged with three sets of contact points,
thus permitting any one of three Morse registers, shown in the
photograph, Fig. 308, to be operated at will. Three series of waves
jiJ... .r-..,*.. .1...'. i
m
f r f r r « '
FIG. 309. — TAPE OF BULL SYSTEM.
were used, represented in A, Fig. 309, by the dotted lines S*t S2, S*,
the horizontal line being taken as time and the wave series by the
heavy vertical strokes. The spaces between the light strokes rep-
resent intervals of one-fifth second. B illustrates how the wave
series are registered when the key of the transmitter is kept closed.
I, II, III, are the types of three Morse registers operated
independently of each other. The transmitters and receivers
284 WIRELESS TELEGRAPHY
may be set up in different localities and at varying distances with
equally good results.
This represents the evolution of transmitting messages through
space without wires as well as the wireless transmission of intelli-
gence in the same field of force without interference. Wireless
telegraphy has made gigantic strides since its inception a few years
ago, especially in the bridging of distance, but its commercial future
now rests on the problem of syntonization, and when this shall have
been accomplished the possibilities of the new art will be practically
unlimited and of untold value.
CHAPTER XX.
WIRELESS TELEPHONY.
The brilliant achievements in wireless telegraphy lead naturally
and in sequence to the more difficult proposition of transmitting
articulate speech without wires ; but wireless telegraphy is infinitely
easier of solution than wireless telephony, since an electrical im-
pulse of any character may be utilized as a signal, whereas in the
transmission of speech an alternating current having the same
phase, amplitude and frequency at either station are neces-
sary. This being the case, it is obvious that electric waves produced
by the disruptive discharge are not suitable for wireless telephony,
--»• c
B •«•
Fio. 310. — ELLIPTICAL LINES OP FORCE.
Fro. 311. — CONDUCTIV-
ITY METHOD.
since the decrement of the oscillations producing the waves are
periodic and reach 0 in a very small fraction of a second, and are,
therefore, quite incompatible with the long, smooth sine wave cur-
rents usually employed in telephony. But while electric waves are
not adapted to wireless telephony there are several methods by which
results may be obtained within certain limitations.
285
286
WIRELESS TELEGRAPHY.
CONDUCTIVITY METHOD. — One of the simplest methods of tele-
phoning without wires is by utilizing the earth as a portion of the
sending and receiving circuits, and by leakage or dispersion of the
current in the primary circuit through the earth the energy spreads
in elliptical lines of force like magnetic lines between the poles of
a magnet, as in Fig. 310. This is known as the conductivity
method, and when applied to actual transmission two base lines,
AB and CD, are arranged parallel with each other so that the
terminals of the sending and receiving circuits are earthed, as shown
in Fig. 311, when a current, either direct or alternating, flows
through the circuit AB the energy is propagated to the circuit CD
in virtue of the great cross-section of the earth, which is a fairly
good conductor. The length of the base lines should be, preferably,
twice the length of the distance to which speech is to be transmitted ;
FIG. 312. — INDUCTIVITY METHOD.
it is this limiting feature which has prevented its employment in
practice, except, perhaps, in special cases.
INDUCTIVITY METHOD. — A second fundamental method ideal
in its mode of propagating energy when articulate speech is con-
sidered, consists of a large primary coil of wire with a similar
secondary placed at a distance. Let AB, Fig. 312, represent two
coils of wire placed with their planes parallel with each other, or
their planes may be horizontal. On speaking into a telephone
transmitter with a battery in series with the coil A an undulatory
current in rotation through the turns of wire will set up a magnetic
flux the lines of which may be great enough to link the coil B,
i.e., when the lines from the coil A thread through the coil B an
e. m. f. proportional to the rate at which they link with the coil
B produces by its inductive action a momentary current in the
coil including in its circuit the telephone receiver. As the num-
WIRELESS TELEPHONY. 287
ber of turns of wire and size of the coils and e. m. f. increases the
distance between the two coils may be extended.
ELECTRIC WAVE METHOD. — Many experimenters have en-
deavored to utilize high-frequency, high-potential currents in wire-
less telephony, but, for reasons previously pointed out, it is not
practicable to employ a disruptive discharge to obtain electric
oscillations of constant value. Alternating currents, however, of
comparatively low frequency will emit electric waves, although such
radiations are very feeble ; but speech may be transmitted wirelessly
if the spark-gap of the oscillator is bridged by an air-gap and a
mechanically high-frequency current is employed ; the spoken words
will be reproduced by inserting a receiver in the resonator circuit.
Another method the author has employed is to permit the spark-
gap of the oscillator to remain open, causing the current to surge
to and fro in it with every reversal in the secondary of the trans-
former, although it is difficult to determine whether the calcula-
tions obtained are the result of an alternating magnetic field
\/ o /
6^c
FIG. 313. — BELL RADIOPHONE.
around the radiator or electric waves . emanating from it. This
method offers some promise, though the effective distance covered
has been exceedingly limited.
BELL KADIOPHONE. — The principles upon which Professor
Alexander Graham BelPs radiophone for telephoning by a beam
of light are well known. In this method a ray of light
from either the sun or an arc light is caused to fall upon a plane
mirror, 1, Fig. 313, and reflected to the lens, 2, where it is re-
fracted and brought to a point and impinges on the concave mir-
ror, 3, attached to the back of a diaphragm of a telephone trans-
mitter, 4; the light, after reflection from the mirror, 3, passes
through a condensing lens, 5, where it is projected to a distance
288
WIRELESS TELEGRAPHY.
through space to the receiver, 6. This consists of a parabolic
mirror, af having a selenium cell, I, placed in its focal line; a
battery, d, and a telephone receiver, c, are connected in series with
the selenium cell.
When the radiophone is in action the vibrations of the dia-
phragm by the voice varies the intensity of the light falling upon
the concave mirror and the projected beam of light is gathered in
the focus of the receiving parabolic mirror, where the light waves
are concentrated on the selenium cell, which varies in resistance
FlG. 314. KUHMKR PHOTO- Kl.KCTKlC 1'UANUMITTKR.
coincidently with the intensity variations of the light, and every
vibration of the diaphragm, change in light intensity and cell resist-
ance is reproduced in the telephone receiver. Speech has been trans-
mitted by this method several hundred feet and is marvelously clear
and distinct.
EUHMER PHOTO-ELECTRIC TELEPHONE. — Since Bell's experi-
ments, new discoveries have been made in photo-electric effects,
and among the most interesting may be cited the speaking arc,
invented by Simon, of Gottingen, Germany, who ascertained
that by superimposing an alternating current, induced in the sec-
ondary of a small transformer coil by the undulations of the pri-
mary in series with a telephone transmitter, as a heavy direct-cur-
rent operating an arc light the volume and intensity of the flame
WIRELESS TELEPHONY.
289
varied proportionately, and though these variations ,/ere not per-
ceptible to the eye, due to the persistency of vision, they would
affect a photographic plate or a selenium cell.
Having in view the object of producing a photo-electric tele-
FIG. 315.— RUHMER PHOTO-ELECTRIC RECEIVER.
phone of sufficient penetrative power to be useful, Professor Ernest
Ruhmer, of Berlin, devised an apparatus for utilizing the principles
involved in Bell's radiophone and the Simon speaking arc. This
he did by placing an arc light in the focal line of a parabolic re-
flector, Fig. 314, having a diameter of 50 cm., and constructed like
290
WIRELESS TELEGRAPHY.
a searchlight. The arc is supplied by a storage battery of 52
and 8 or 10 amperes when speech was transmitted over a distance
of 3 or 4 kilometers. A telephone transmitter is connected in series
with a small storage battery of 6 or 8 volts, as shown in the illus-
tration, and the primary of a transformer, while the secondary is
connected through a condenser in parallel with the arc-light circuit.
The receiver designed by Euhmer, Fig. 315, consists of a parabolic
reflector and having a selenium cell placed in its focal line in
series with a pair of telephone receivers and a battery. Selenium
FIG. 316. — RUHMER'S ELECTRIC LAUNCH "THE GKKMANIA."
cells, employed before Euhmer, were made by winding a pair of wires
parallel to each other on a flat piece of glass and filling the space
between them with fused selenium. Clausen and von Bronk made a
cell of this type having a ratio of 10 to 1 in resistivity variations,
and a cell by Giltay exhibited a variation ranging between 533.000
ohms in darkness to 26,000 ohms in a light of 400 intensity, but
these cells have a high time constant in returning to their original
resistance. The cell devised by Euhmer was given a cylindrical
form so that the light might be evenly distributed over its surface
by the reflector. The selenium cell was made by winding two fine
platinum wires in parallel and separated by 7-10 mm. on a glass
tube 33 mm. in length and 20 mm. in circumference and then fore-
WIRELESS TELEPHONY. 291
ing the prepared selenium in the space between the wires. This
preparation consists of heating the amorphous red powder, in which
state selenium is found, until it is transformed into a black, gummy
mass, when it becomes a very good insulator ; it is then applied to
the interstices of the platinum wires and baked for twelve hours at
Fio. 317. — RUHMER RECEIVING A PHOTO-ELECTRIC MESSAGE.
a constant temperature of 200° F., when it is annealed by gradually
reducing the temperature and crystalline selenium results, having
a gray color and assuming the remarkable property of varying its
electrical resistance under the influence of light. Such a cell is
marvelously sensitive to light variations and has a maximum re-
292 WIRELESS TELEGRAPHY.
sistance of 120,000 ohms in the dark and dropping to 1,500 ohms
when illuminated by a 1G candle-power lamp. With this equipment
liuhmer conducted his experiments on Wannsee, the transmitter
being placed on an electric launch, the Germaniaj Fig. 31G, and the
receiver on the shore, Fig. 317, at a distance of ll/2 kilometers; this
distance was gradually increased until a maximum distance of 4
kilometers was reached.
COLLINS WIRELESS TELEPHONE. — Having tested all the above
methods for transmitting articulate speech without wires, and
finding that each had its especial limitations, the author sought for
some method by which the difficulties encountered might be over-
come. In experiments with coherers adjusted to their maximum
sensitiveness it was ascertained that comparatively low-frequency,
high-potential currents alternating through an oscillator would emit
waves of sufficient energy to break down the resistance of a de-
tector. It was also found that when mechanically produced high-
frequency, high-potential currents are discharged into the earth
and there restore the potential level of the circuit, of which the
earth forms a portion, instead of free air, new manifestations occur,
and among them may be cited the propagation of long sine waves
to great distances. The length of the waves depends on the fre-
quency of alternations and the frequency on the coefficients of the
transmitting circuit, and these joint factors, finally on the constants
of the ether, which are its elasticity and its density.
Since the value of elasticity of the ether is not absolutely known,
it has been determined empirically by its reciprocal or dielectric
constant, as when ether is associated with gross matter which has
a specific inductive capacity. The density of ether closely identified
with the atoms of the atmosphere, acts, paradoxically, as though
it were greater than in vacuo, and the effect on the particles of
matter of which the earth is composed is greater than on the air.
The term bound ether has been given to ether associated with gross
matter. Now matter, gross or transcendental, acts like a solid
body if it is struck hard enough, when vibrations will be trans-
mitted by it. Strike the surface of a body of water with a board and
it will assume at the instant of impact all the characteristics of a
solid ; and every molecule of the water will vibrate in consequence ;
beat the air with an outspread wing with sufficient force and it will
resist its movement, if its velocity is great enough, like a solid
body, and the ether also acts like a solid body if it is struck hard
WIRELESS TELEPHONY.
293
enough and an electric discharge is the hammer to strike it with,
when transverse vibrations in it occur.
Mechanically high-frequency, high-potential currents cause the
earth-bound ether to manifest its presence to a greater distance than
in free ether or ether associated with air upon the impact of the
former. The action of sound waves furnishes a good analogue; if
a bell is struck in water it can be heard many times farther than
when it is struck in free air, for the density of water is greater than
air ; similarly if a bell could be struck in a sea of mercury the sound
waves would be propagated to a much greater distance than in
Fio. 318. — COLLINS SENDING A WIRELESS TELEPHONE MESSAGE.
water, since mercury is much more dense than water. The waves
the author employed in his wireless telephone are radiated normally
in a circle, but it has been found possible to reflect and make them
undirectional within 15° of arc. Fig. 318 is an illustration of a
portable equipment devised for testing the telephone in the field,
and was employed in the early experiments. Later, three stations,
Figs. 319, 320 and 321, were established at Rockland Lake, N. Y.
Complete standard station sets were installed at these stations for
wireless telephony, as shown in Fig. 322. In the transmitter a
primary coil is connected in series with a key, battery, and variator ;
the terminals of the secondary winding are connected to a circuit cor-
29-4
WIRELESS TELEGRAPHY.
responding to the oscillator of a wireless telegraph system. Bridged
across the secondary of the transformer coil is an adjustable con-
denser, so that the ratio of inductance and capacity may be main-
tained in their proper relations and the reproduced speech made
clear and distinct. The receiver operates through a circuit similar
FIG. 319. — COLLINS WIRELESS TELEPHONE STATION A.
to a resonator and consists, in its simplest form, of a telephone
receiver, a battery, transformer, coil, inductance, and capacity.
When in operation and the primary circuit is closed, the current
is varied automatically, and mechanically high frequency and high
potential currents are set up in the discharging circuit, which emit
the waves in the earth ; the waves impinging on the receiving circuits
surge with the same frequency and have the same amplitude of
vibration, though diminished volume of the original currents of the
WIRELESS TELEPHONY.
295
FIG. 320. — COLLINS WIRELESS TELEPHONE STATION I*.
FIG. 321. — COLLINS WIRELESS TELEPHONE STATION C.
296
WIRELESS TELEGRAPHY.
emitting circuits. The received impulses are translated by a tele-
phone receiver. The first tests of this system of wireless telephony
were made at Philadelphia, Pa., in 1899, when speech was trans-
FIG. 322.— THK "JOHN G. MCCULLOUGH
FIG. 332. — COLLINS WIRELESS TELEPHONE.
mitted to a distance of 200 feet; in 1900 words were sent wire-
lessly across the Delaware River, a mile, and in 1902, with im-
proved apparatus, a distance of three miles was covered between
the sending and receiving stations. In the same year proving sta-
WIRELESS TELEPHONY. 297
tions were established at Kockland Lake, N. Y., A, Bf Figs. 320 and
321 being a mile apart. This was the first complete wireless tele-
phone system working in both directions and equipped with signal-
ing apparatus.
While these preliminary tests have been made on land, the
sphere of the wireless telephone lies in its application to vessels
in harbors. Hardly a month passes but that one vessel rams an-
other, due primarily to a misunderstood signal, and this is especially
true in foggy weather.
The wireless telegraph is not adapted to this class of work, since
it requires a skilled operator who must be constantly at the cap-
tain's or pilot's side to interpret the Morse code. The wireless
telephone is a first-hand instrument at once simple, reliable, and
may be applied to any vessel at a comparatively small cost. Ex-
tensive experiments have been in progress during the summer on
the Hudson River (New York City), where wireless telephones were
installed on the ferryboats John G. McCuLlougli and Ridgewood,
of the Erie Railroad system, pictures of which are given in Fig. 323.
Not until the advent of the wireless telephone had there been a
single improvement looking toward the safety factor in marine
signaling at close range since the invention of the time-honored and
hoary steam whistle.
Into the future it is dark and difficult to see! Its misty veil
is so drawn that only a little light reaches us through its filtering
meshes, and this by the empirical path of experience; therefore we
cannot predict. The wireless telegraph, the dream of yesterday, is a
reality of to-day; cableless telegraphy, now in its experimental
struggles, may eliminate the cable to-morrow. The wireless tele-
phone may never supplant the efficient wire-system, yet stranger
things have come to pass in less time than the quarter of a cycle
we term a century. The assistance of the telegraph, the cable, the
telephone in the advancement of civilization is beyond the wildest
speculation of the romancer living fifty years ago. What these
modes for the transmission of intelligence have done for mankind
in the making the last half of the past century let us hope that
wireless methods will do for the first half of the present century.
These are but additional links in the universal chain of evolution
as designed by the omnipotent Creator.
INDEX TO NAMES.
Allemaod, 37.
Ampere, 78, 79.
Apps, 37, 95.
Arago, 78.
Arco, passim.
Arons, 148.
Ascoli, 236, 237.
Bachhoffer, 92, 93.
Baden-Powell, 252.
Barker, 93.
Becquerel, G6, 79.
Bell, 228, 287, 289.
Beckeley, 6.
Bernouilli, 2GO.
Bichat, 112, 114.
Bjerknes, 21, 52, 148, 258, 264, 265.
Blondel, passim.
Boltzmann, 148.
Bononio, 237.
Boscovitch, 2, 3.
Bose, 127, 139.
Botts, 66.
Bradley, 14.
Braun, passim.
Bra illy, passim.
Bronk, von, 290.
Bull, 164, 183, 186, 207, 270, 280.
Caldwell, 100, 119.
Callan, 92, 93.
Calzecchi-Onesti, 136, 137, 141, 145.
Cardew, 148.
Castelli, 154.
Cervera-Baveria, 182, 202, 203.
Claude, 203.
Clausen, 2»0.
Collins, passim.
Coulomb, (54.
Cunningham, 114, 115.
Davy, 78, 211.
De Forest, passim.
De la Rive, 21, 24, 25.
Dolbear, 234.
Dunne, 27.
Dubois-Reymond, 79.
Ducretet, 'passim.
Eccle. 138.
Eddy, 240.
Edison, 171, 234.
Edlund, 65.
Erlung, 10.
Ewing, 84.
Faraday, passim.
Fedderson, 37, 48.
Felici, 79.
Fessenden, passim.
Fitzgerald, 20, 148.
Fizeau, 14, 79, 94..
Fleming, passim.
Foote, 102.
Foucault, 14, 79.
Franklin, 36, 37.
Fresnel, 9.
Geissler, 27, 101.
Gilbert, 47.
Giltay, 290.
Green, 64.
Gregory, 148.
Grisson, 100, 122, 124.
Guarini-Foresio, passim.
Guericke, von, 36, 127.
Guitard, 136.
Guthe, 139, 142.
Haeckle, 6.
Halske, passim.
Hawksbee, 36.
Heardon, 139.
Heaviside, 21.
Helmholtz, von, passim.
Henry, passim.
Hertz, passim.
Hewitt, 125.
Holtz, 127, 129.
Hopkinson, 55.
Hughes, 136.
Hume, 6.
Huygens, 2, 3, 14.
Ives, 76, 86, 96.
Jaumann, 39, 44.
Jean, 94.
Jegou. 241.
Jenkins, 65.
Johnson, 87.
Jones, 7.
Joulo, 66, 69.
INDEX TO NAMES.
299
Kelly, 258.
Kelvin, passim.
Kinraide, 103.
Kinsley, 143, 144.
Kintner, 137, 154.
Kirehhoff, 60, 79.
Kitsee, 234.
Kleist, 36.
Klingelfuss, 88, 89, 90.
Koepsel, 142, 151, 234.
Koosen, 258.
La Grange, 3.
Lamb, 59.
Langley, 27.
La Place, 64.
Lebedew, 8, 21, 33.
Lecher, 27.
Lenz, 66, 79, 258.
Lodge, passim.
Marchant, 48.
Marconi, passim.
Martin, 130, 212.
Matthieson, 66.
Maxwell, passim.
Mizinro, 90.
Morse, passim.
Muirhead, passim.
Murphy, 121, 122.
Musschenbroek, 36.
Neef, 94, 109.
Neugschwender, 137.
Neumann, 79, 236.
Newton, 2, 13.
Ohm, 49, 66, 68, 69.
Overbeck, 258.
Paalzow, 148.
Page, 92, 94.
Pierson, 102.
Plank, 54.
Plato, 9.
Poggendorf, 93.
Poincaire, 21.
Poisson, 64.
Popoff, passim.
Popp, 180, 203, 207.
Poynting. 21.
Preece, 82.
Pupin, 11, 258.
Queen, 42, 105.
Rayleigh, 55, 86.
Reiss, 22, 46, 52.
Righi, 58, 148, 153, 238.
Ritchie, 79.
Ritter, 142, 148.
Romer, 14.
Rontgen, 15.
Rubens, 148.
Ruhmer, 288, 289, 290, 292.
Ruhmkorff, 37, 79, 94, 169.
Rutherford, 137, 185.
Sarasin, 24, 25.
Savart, 47, 48.
Schaffer, 137, 153.
Shaw, 139.
Siebt, 261.
Siemens, passim.
Silliman, 92.
Simon, 175, 288, 289.
Slaby, passim.
Smythe, 143, 201.
Spottiswood, 37, 95.
Sprague, 99.
Stone, 164, 277.
Sturgeon, 78, 92.
Taylor, 33.
Tesla, passim.
Thompson, Sylvan us, 17, 20.
Thomson, Elihu, passim.
Thomson, J. J., 21, 59.
Toepler, 127, 129.
Tommasini, 142.
Trowbridge, 27, 37, 48, 139.
Turpain, 59.
Tyndall, 13, 48.
Varley, 136.
Wagner, 79, 94.
Watson, 36.
Weber, 79.
Wehnelt, 40, 116, 119.
Wheatstone, 14, 66, 77.
Wiedemann, 29, 44.
Willyoung, 116.
Wilson, 55.
Young, 14.
Zehnder, 147.
OF THE
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